Image synthesizing apparatus, iris authentication system, image synthesizing method, and iris authenticating method

ABSTRACT

An image synthesizing apparatus includes an illuminating device that outputs linearly polarized light having a first polarization direction and linearly polarized light having a second polarization direction, a camera that captures an image in a third polarization direction including a plurality of pixels and an image in a fourth polarization direction including a plurality of pixels, and a control circuit that synthesizes, on a pixel-by-pixel basis, the image in the third polarization direction and the image in the fourth polarization direction into an authentication image for iris authentication. The first, the second, the third and the fourth polarization directions are different from one another. The camera acquires the image in the third polarization direction using the linearly polarized light in the first polarization direction and acquires the image in the fourth polarization direction using the linearly polarized light in the second polarization direction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of Japanese PatentApplication Number 2018-035941 filed on Feb. 28, 2018, the entirecontent of which is hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an image synthesizing apparatus, aniris authentication system, an image synthesizing method, and an irisauthenticating method.

2. Description of the Related Art

In recent years, authentication techniques for performing personalauthentication from a face of a person imaged by a camera have rapidlyprogressed. As one of such authentication techniques, there is an irisauthentication technique. The iris authentication technique is a methodwith an extremely low rate of erroneously recognizing another person asa person in question (false accept rate FAR). For example, JapanesePatent No. 3307936 (Patent Literature 1) discloses a technique forextracting an iris in an image of a face of a person and determiningidentity of the iris from similarity between a code of the iris and acode of a reference iris. Japanese Patent No. 3586456 (Patent Literature2) discloses an iris authentication technique for preventingdeterioration in authentication accuracy due to reflection of externallight on an iris. Specifically, authentication of an iris image withrespect to registered iris data is performed using a plurality of irisimages in which reflecting positions of external light are different andthe registered iris data.

Related art is also disclosed in Yuichi Ichihashi, Shuichi Kawabata,Kazuo Ishikawa, and Toyohiko Hatada, “Polarization Characteristics in anEyeball Imaging System and an Analysis of the PolarizationCharacteristics”, Journal of Japanese Ophthalmological Society, 1989,Volume 10, No. 1, p. 87 to 92 (Non Patent Literature 1) The technique ofPatent Literature 1 does not consider reflection of external light on aniris. In the technique of Patent Literature 2, a direction of a face ofa person in photographing an iris image is designated. Both of thetechniques target a limited iris image and are not considered to havehigh iris authentication accuracy.

SUMMARY

Therefore, the present disclosure provides an image synthesizingapparatus, an iris authentication system, an image synthesizing method,and an iris authenticating method for improving iris authenticationaccuracy.

An image synthesizing apparatus according to an aspect of the presentdisclosure includes: an illuminating device that outputs linearlypolarized light having a first polarization direction and linearlypolarized light having a second polarization direction; a camera thatcaptures an image in a third polarization direction including aplurality of pixels and an image in a fourth polarization directionincluding a plurality of pixels; and a control circuit that synthesizes,on a pixel-by-pixel basis, the image in the third polarization directionand the image in the fourth polarization direction into anauthentication image for iris authentication, wherein the firstpolarization direction, the second polarization direction, the thirdpolarization direction, and the fourth polarization direction aredifferent from one another, and the camera acquires the image in thethird polarization direction using the linearly polarized light in thefirst polarization direction and acquires the image in the fourthpolarization direction using the linearly polarized light in the secondpolarization direction.

An image synthesizing apparatus according to an aspect of the presentdisclosure includes: an illuminating device that outputs linearlypolarized light having a first polarization direction and linearlypolarized light having a 10 second polarization direction; a camera thatcaptures an image in a third polarization direction including aplurality of pixels and an image in a fourth polarization directionincluding a plurality of pixels; and a control circuit that synthesizes,on a pixel-by-pixel basis, the image in the third polarization directionand the image in the fourth polarization direction into anauthentication image for iris authentication, wherein the firstpolarization direction and the second polarization direction aredifferent from each other, the third polarization direction and thefourth polarization direction are different from each other, and thecamera acquires the image in the third polarization direction using thelinearly polarized light in the first polarization direction and thelinearly polarized light in the second polarization direction andacquires the image in the fourth polarization direction using thelinearly polarized light in the first polarization direction and thelinearly polarized light in the second polarization direction.

An image synthesizing apparatus according to an aspect of the presentdisclosure includes: an illuminating device that outputs rightcircularly polarized light and left circularly polarized light; a camerathat captures an image in a right polarization direction including aplurality of pixels and an image in a left polarization directionincluding a plurality of pixels; and a control circuit that synthesizes,on a pixel-by-pixel basis, the image in the right polarization directionand the image in the left polarization direction into an authenticationimage for iris authentication, wherein the camera acquires the image inthe right polarization direction using the right circularly polarizedlight and the left circularly polarized light and acquires the image inthe left polarization direction using the right circularly polarizedlight and the left circularly polarized light.

An image synthesizing apparatus according to an aspect of the presentdisclosure includes: an illuminating device that simultaneously outputsfirst linearly polarized light having a first polarization direction,second linearly polarized light having a second polarization direction,third linearly polarized light having a third polarization direction,and fourth linearly polarized light having a fourth polarizationdirection; a camera that captures a fifth image in the firstpolarization direction including a plurality of pixels, a sixth image inthe second polarization direction including a plurality of pixels, aseventh image in the third polarization direction including a pluralityof pixels, and an eighth image in the fourth polarization directionincluding a plurality of pixels; and a control circuit that synthesizes,on a pixel-by-pixel basis, the fifth image, the sixth image, the seventhimage, and the eighth image into an authentication image for irisauthentication, wherein the first polarization direction, the secondpolarization direction, the third polarization direction, and the fourthpolarization direction are different from one another by 45 degrees, andthe camera acquires the fifth image, the sixth image, the seventh image,and the eighth image respectively using the first linearly polarizedlight, the second linearly polarized light, the third linearly polarizedlight, and the fourth linearly polarized light.

An iris authentication system according to an aspect of the presentdisclosure includes: the image synthesizing apparatus according to theabove aspect; and an iris authentication circuit, wherein the irisauthentication circuit acquires iris authentication information in whicha plurality of user identifications (IDs) and a plurality of referenceimages are associated with each other and identifies a user ID withreference to the authentication image and the iris authenticationinformation.

An image synthesizing method according to an aspect of the presentdisclosure includes: sequentially outputting first linearly polarizedlight having a first polarization direction and second linearlypolarized light having a second polarization direction; when the firstlinearly polarized light is output, capturing an image to acquire athird image in a third polarization direction including a plurality ofpixels; when the second linearly polarized light is output, capturing animage to acquire a fourth image in a fourth polarization directionincluding a plurality of pixels; and synthesizing, on a pixel-by-pixelbasis, the third image and the fourth image into an authentication imagefor iris authentication, wherein the first polarization direction, thesecond polarization direction, the third polarization direction, and thefourth polarization direction are different from one another, and atleast one of the sequential outputting, the capturing of the image toacquire the third image, the capturing of the image to acquire to thefourth image, and synthesizing is executed by at least one controlcircuit.

An image synthesizing method according to an aspect of the presentdisclosure includes: outputting first linearly polarized light having afirst polarization direction and second linearly polarized light havinga second polarization direction together; capturing an image when thefirst linearly polarized light and the second linearly polarized lightare output; acquiring, from the image, a third image in a thirdpolarization direction including a plurality of pixels and a fourthimage in a fourth polarization direction including a plurality ofpixels; and synthesizing, on a pixel-by-pixel basis, the third image andthe fourth image into an authentication image for iris authentication,wherein the first polarization direction and the second polarizationdirection are different from each other, the third polarizationdirection and the fourth polarization direction are different from eachother, and at least one of the outputting, the capturing the image, theacquiring, and synthesizing is executed by at least one control circuit.

An image synthesizing method according to an aspect of the presentdisclosure includes: outputting right circularly polarized light andleft circularly polarized light together; capturing an image when theright circularly polarized light and the left circularly polarized lightare output; acquiring, from the image, an image in a right polarizationdirection including a plurality of pixels and an image in a leftpolarization direction including a plurality of pixels; andsynthesizing, on a pixel-by-pixel basis, the image in the rightpolarization direction and the image in the left polarization directioninto an authentication image for iris authentication, wherein at leastone of the outputting, the capturing, the acquiring, and synthesizing isexecuted by at least one control circuit.

An image synthesizing method according to an aspect of the presentdisclosure includes: simultaneously outputting first linearly polarizedlight having a first polarization direction, second linearly polarizedlight having a second polarization direction, third linearly polarizedlight having a third polarization direction, and fourth linearlypolarized light having a fourth polarization direction; capturing animage when the first linearly polarized light, the second linearlypolarized light, the third linearly polarized light, and the fourthlinearly polarized light are output; acquiring, from the image, a fifthimage in the first polarization direction including a plurality ofpixels, a sixth image in the second polarization direction including aplurality of pixels, a seventh image in the third polarization directionincluding a plurality of pixels, and an eighth image in the fourthpolarization direction including a plurality of pixels; synthesizing, ona pixel-by-pixel basis, the fifth image, the sixth image, the seventhimage, and the eighth image into an authentication image for irisauthentication, wherein the first polarization direction, the secondpolarization direction, the third polarization direction, the fourthpolarization direction are different from each other by 45 degrees, andat least one of the simultaneously outputting, the capturing, theacquiring, and synthesizing is executed by at least one control circuit.

An iris authenticating method according to an aspect of the presentdisclosure includes: acquiring the authentication image generated by theimage synthesizing method according to the above aspect; acquiring irisauthentication information in which a plurality of user IDs and aplurality of reference images are associated with each other;identifying a user ID with reference to the authentication image and theiris authentication information, wherein at least one of the acquiringof the authentication image, the acquiring of the iris authenticationinformation, and the identifying is executed by at least one controlcircuit.

The comprehensive and specific forms explained above may be realized asa system, an apparatus, a method, an integrated circuit, a computerprogram, or a computer-readable recording medium such as a recordingdisk or may be realized as any combination of the system, the apparatus,the method, the integrated circuit, the computer program, and therecording medium. The computer-readable recording medium includes anonvolatile recording medium such as a CD-ROM (Compact Disc-Read OnlyMemory).

With the image synthesizing apparatus and the like of the presentdisclosure, it is possible to improve iris authentication accuracy.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram showing an example of a functionalconfiguration of an iris authentication system according to the firstembodiment;

FIG. 2 is a schematic diagram showing an example of a flow of processingby components of the iris authentication system according to the firstembodiment;

FIG. 3 is a schematic front view of an illuminating device according tothe first embodiment;

FIG. 4A is a plan view schematically showing the configuration of apolarization imaging element of a camera according to the firstembodiment;

FIG. 4B is a plan view showing one unit of a group of polarizing filtersin a mosaic polarizing filter shown in FIG. 4A;

FIG. 5A is a schematic diagram showing a situation in which environmentlight and illumination light are specularly reflected on a cornea or aneyeglass;

FIG. 5B is a front view of the eyeglass in FIG. 5A;

FIG. 5C is a front view of the cornea in FIG. 5A;

FIG. 6 is a diagram showing a removal characteristic of specularreflection of the environment light in a band-pass filter;

FIG. 7A is a diagram showing a generation state of specular reflectionof the illumination light in the cornea right opposed to the camera;

FIG. 7B is a diagram showing a generation state of specular reflectionof the illumination light in the eyeglass and the cornea right opposedto the camera;

FIG. 7C is a diagram showing a generation state of specular reflectionof the illumination light in the cornea obliquely facing the camera;

FIG. 8A is a schematic diagram for explaining a birefringence phenomenonin the cornea and is a schematic diagram showing a situation in whichlinearly polarized illumination is made incident and reflected on thecornea;

FIG. 8B is a diagram for explaining the birefringence phenomenon in thecornea and is a schematic front view showing the linearly polarizedlight illumination made incident on the cornea;

FIG. 8C is a diagram for explaining the birefringence phenomenon in thecornea and is a schematic front view showing the linearly polarizedillumination reflected on the cornea;

FIG. 9 is a diagram schematically showing an example of a generationstate of a black cross pattern in the cornea;

FIG. 10A is a diagram showing an example of a pattern for generating ablack cross using a convex lens that changes according to a polarizationdirection;

FIG. 10B is a diagram showing an example of a pattern for generating ablack cross using the convex lens that changes according to thepolarization direction;

FIG. 11A is a schematic diagram showing an example of processing of apolarized image synthesizer for removing the black cross pattern;

FIG. 11B is a diagram showing an example of a periodic functionindicating a principle of black cross pattern removal by the processingof the polarized image synthesizer;

FIG. 12 is a flowchart showing an example of the operation of the irisauthentication system according to the first embodiment;

FIG. 13 is a block diagram showing an example of a functionalconfiguration of an iris authentication system according to a secondembodiment;

FIG. 14 is a schematic diagram showing an example of a flow ofprocessing by components of the iris authentication system according tothe second embodiment;

FIG. 15A is a schematic front view of an illuminating device accordingto the second embodiment;

FIG. 15B is a schematic exploded view of the illuminating device shownin FIG. 15A;

FIG. 16A is a plan view schematically showing the configuration of apolarization imaging element of a camera according to the secondembodiment;

FIG. 16B is a plan view showing one unit of a group of polarizingfilters in a mosaic polarizing filter shown in FIG. 16A;

FIG. 17 is a schematic diagram showing a polarization state of reflectedlight at a bright spot of a specular reflection region in a cornea;

FIG. 18 is a schematic diagram showing a polarization state of reflectedlight in a diffuse reflection region in an iris;

FIG. 19 is a schematic diagram showing an example of processing of thepolarized image synthesizer for removing a bright spot of specularreflection;

FIG. 20A is a diagram showing, as in FIG. 2, an example of an irisauthenticating apparatus of related art that performs irisauthentication using circularly polarized light;

FIG. 20B is a diagram schematically showing details of an optical systemshown in FIG. 20A;

FIG. 21 is a block diagram showing an example of a functionalconfiguration of an iris authentication system according to a thirdembodiment;

FIG. 22 is a schematic diagram showing an example of a flow ofprocessing by components of the iris authentication system according tothe third embodiment;

FIG. 23A is a schematic front view of an illuminating device accordingto the third embodiment;

FIG. 23B is a schematic exploded view of the illuminating device shownin FIG. 23A;

FIG. 24A is a plan view schematically showing the configuration of apolarization imaging element of a camera according to the thirdembodiment;

FIG. 24B is a plan view showing one unit of a group of polarizingfilters in a mosaic polarizing filter shown in FIG. 24A;

FIG. 25 is a diagram schematically showing a configuration in amodification of the polarization imaging element according to the thirdembodiment;

FIG. 26 is a schematic diagram showing an example of processing of apolarized image synthesizer for removing a bright spot of specularreflection;

FIG. 27 is a block diagram showing an example of a functionalconfiguration of an iris authentication system according to a fourthembodiment;

FIG. 28 is a schematic diagram showing an example of a flow ofprocessing by components of the iris authentication system according tothe fourth embodiment;

FIG. 29 is a schematic front view of an illuminating device according tothe fourth embodiment;

FIG. 30A is a plan view schematically showing the configuration of animaging sensor of a camera according to the fourth embodiment;

FIG. 30B is a plan view showing one unit of a group of polarizingfilters in a mosaic polarizing filter shown in FIG. 30A; and

FIG. 31 is a schematic diagram showing an example of processing of apolarized image synthesizer for removing a bright spot of specularreflection.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[Knowledge of the Inventor]

First, knowledge of the inventor is explained. As explained in thebackground, in recent years, a face recognition technique for performingpersonal authentication from a face of a person imaged by a camera hasattracted attention and rapidly progressed. As a method ofauthenticating a person, there are techniques for authenticating aperson using various kinds of biometrics such as fingerprintauthentication, vein authentication, and retina authentication. However,in recent years, among various kinds of face authentication, a requestfor a casual authentication technique has been increasing. The casualauthentication means authenticating a person to be authenticated in anunaware state who does not take a predetermined position, apredetermined direction, a predetermined posture, and the like withrespect to an authenticating apparatus. In the casual authentication ofa face, there is an increasing need for a technique for authenticating aperson to be authenticated unaware of a camera by imaging the person tobe authenticated with a camera in a noncontact manner from a distance ofseveral meters. However, in the face authentication, wrong recognitiondue to hiding of a face by a mask or the like or fluctuation of a facedue to extreme facial expression could occur. Further, in the faceauthentication, it is sometimes difficult to distinguish an extremelysimilar face such as faces of twins. That is, in the faceauthentication, there is an essential problem that another person iseasily misrecognized as a person in question.

Therefore, the inventor focused on an iris authentication techniqueconventionally used as a method with an extremely low false accept rateFAR, which is a rate of misrecognition of another person as a person inquestion, and examined highly accurate casual authentication performedby combining the iris authentication technique and the faceauthentication. For example, an iris authentication pattern is obtainedby carrying out special frequency emphasis processing on an iris imagecaptured by a camera. Such an iris authentication pattern is imageinformation having extremely high randomness. In the field of the irisauthentication technique, the iris authentication pattern is consideredto have an FAR of 1/10000 even in the entire population on the Earth.Therefore, in the iris authentication technique using the irisauthentication pattern, another person is never misrecognized as aperson in question even in the case of eyes of twins. In the irisauthentication pattern, fluctuation due to aged deterioration, injury,and the like in an individual is little. An authentication function canbe maintained.

Patent Literature 1 discloses a basic technique in the irisauthentication technique in the past. In the technique, first, a pupilcenter and an iris center are detected from an eyeball image. The pupiland the iris are modeled as circles having different centers andradiuses. Subsequently, a doughnut-shaped iris image is developed into arectangular image using a polar coordinate axis set in the pupil centerand is converted into a binary iris authentication pattern using a Gaborfilter or the like. Authentication processing is determined according toa humming distance of a signal between iris authentication patterns.

The iris authentication technique in the past is based on IR (infrared)imaging using IR (infrared) illumination. Reflection of reflected lightof illumination light on an eyeball or an eyeglass during imaging oftenoccurred. For example, Patent Literature 2 discloses an irisauthentication technique adopted when cooperation of a person to beauthenticated during authentication of the person to be authenticatedcan be obtained. In the iris authentication technique of PatentLiterature 2, with active cooperation of the person to be authenticated,an angle and a distance of imaging for the person to be authenticatedare adjusted to prevent unintended reflected light of illumination frombeing reflected on an iris authentication pattern. However, in thecasual iris authentication technique focused by the inventor, while aperson to be authenticated is unaware of IR illumination and an IRcamera, a face image of the person to be authenticated is captured froma far distance using the IR illumination and the IR camera. Irisauthentication is performed using the face image. In this case, even ifIR illumination light reflects on a cornea or a lens of an eyeglass andhides a pupil or an iris of an eyeball, cooperation for avoiding thehiding is not obtained from the person to be authenticated. Therefore,the inventor examined contrivance of illumination light on anilluminating device side and examined irradiation of the person to beauthenticated with linearly polarized light using a polarizer. Further,the inventor examined contrivance on an imaging side and examinedsetting of an analyzer, which is a polarizing plate, in the camera. Theinventor focused on removing reflected light of illumination from animage by making a polarization direction of the linearly polarized lightand a polarization direction of the polarizing plate orthogonal.However, as described in Non Patent Literature 1, in eyeballphotographing using the orthogonal polarization technique explainedabove, a birefringence pattern (called “black cross pattern(Polarization Cross)” as well) of a light and shade stripe shape iscaused by a birefringence characteristic of an originally transparentcornea that covers an iris surface. The birefringence pattern issuperimposed on an original iris pattern. Therefore, iris authenticationfails.

That is, in the casual iris authentication in which cooperation of aperson to be authenticated is not obtained during authentication, apattern of an artifact due to the birefringence characteristic of thecornea appears with respect to an attempt to remove reflection ofillumination light from the cornea and the eyeglass using the linearlypolarized light. Authentication by the iris authentication technique inthe past cannot be performed because of the influence of the pattern.The inventor invented a technique described below in order to enablehighly accurate iris authentication by solving the various problemsdescribed above.

An image synthesizing apparatus according to a first aspect of thepresent disclosure includes: an illuminating device that outputslinearly polarized light having a first polarization direction andlinearly polarized light having a second polarization direction; acamera that captures an image in a third polarization directionincluding a plurality of pixels and an image in a fourth polarizationdirection including a plurality of pixels; and a control circuit thatsynthesizes, on a pixel-by-pixel basis, the image in the thirdpolarization direction and the image in the fourth polarizationdirection into an authentication image for iris authentication, whereinthe first polarization direction, the second polarization direction, thethird polarization direction, and the fourth polarization direction aredifferent from one another, and the camera acquires the image in thethird polarization direction using the linearly polarized light in thefirst polarization direction and acquires the image in the fourthpolarization direction using the linearly polarized light in the secondpolarization direction.

According to the first aspect, in the image in the third polarizationdirection acquired using the linearly polarized light in the firstpolarization direction different from the third polarization direction,an image of specular reflection due to positive reflection in a corneaof an eyeball can be reduced. In the image in the fourth polarizationdirection acquired using the linearly polarized light in the secondpolarization direction different from the fourth polarization direction,the image of the specular reflection in the cornea of the eyeball can bereduced. In the image in the third polarization direction and the imagein the fourth polarization direction in the different polarizationdirections, even when images due to birefringence of the cornea appear,the images can appear in different positions. Therefore, in anauthentication image obtained by combining the image in the thirdpolarization direction and the image in the fourth polarizationdirection, an image of the specular reflection of the cornea and animage due to the birefringence of the cornea are reduced. Therefore, aniris region of the authentication image can be an image suitable forauthentication. For example, the first polarization direction of thelinearly polarized light can be set to 90 degrees and the secondpolarization direction of the linearly polarized light can be set to 135degrees. The third polarization direction of the image can be set to 0degree and the fourth polarization direction of the image can be set to45 degrees.

According to the first aspect of the present disclosure, it is possiblethat the first polarization direction is different from the secondpolarization direction by 45 degrees, that the third polarizationdirection is a linear direction different from the first polarizationdirection by 90 degrees, and that the fourth polarization direction is alinear direction different from the second polarization direction by 90degrees.

According to the first aspect, since the difference between the firstpolarization direction and the third polarization direction is 90degrees, a removal rate of the image of the specular reflection of thecornea in the image in the third polarization direction is improved.Since the difference between the second polarization direction and thefourth polarization direction is 90 degrees, a removal rate of the imageof the specular reflection of the cornea in the image in the fourthpolarization direction is improved. Further, since the differencebetween the first polarization direction and the second polarizationdirection is 45 degrees, a region where the image due to thebirefringence of the cornea is superimposed decreases between the imagein the third polarization direction and the image in the fourthpolarization direction. Accordingly, a removal rate of the image due tothe birefringence of the cornea is improved in an iris region of theauthentication image.

According to the first aspect of the present disclosure, it is possiblethat the illuminating device includes: at least one first light source;at least one second light source; a first polarizing plate having thefirst polarization direction and located in front of the first lightsource; and a second polarizing plate having the second polarizationdirection and located in front of the second light source, that thefirst light source outputs the linearly polarized light having the firstpolarization direction via the first polarizing plate, and that thesecond light source outputs the linearly polarized light having thesecond polarization direction via the second polarizing plate.

According to the first aspect, the linearly polarized light having thefirst polarization direction is irradiated by lighting the first lightsource. The linearly polarized light having the second polarizationdirection is irradiated by lighting the second light source. It is easyto control the irradiation of the linearly polarized light having thefirst polarization direction and the linearly polarized light having thesecond polarization direction.

According to the first aspect of the present disclosure, it is possiblethat when the illuminating device outputs the linearly polarized lightin the first polarization direction, the camera captures the image inthe third polarization direction, and, when the illuminating deviceoutputs the linearly polarized light in the second polarizationdirection, the camera captures the image in the fourth polarizationdirection.

According to the first aspect, it is possible to prevent an unnecessaryimage of linearly polarized light from being included in each of theimage in the third polarization direction and the image in the fourthpolarization direction.

According to the first aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the third polarization direction and the image inthe fourth polarization direction and determines a larger pixel value ofthe pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.

According to the first aspect, a pixel value of the image due to thebirefringence of the cornea decreases in each of the image in the thirdpolarization direction and the image in the fourth polarizationdirection. A larger pixel value among pixel values of pixelscorresponding to each other between the image in the third polarizationdirection and the image in the fourth polarization direction is highlylikely not to be a pixel value of an image due to the birefringence ofthe cornea. By determining such a pixel value as a pixel value of acorresponding pixel in the authentication image, the image due to thebirefringence of the cornea can be effectively removed in theauthentication image.

According to the first aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the third polarization direction and the image inthe fourth polarization direction and determines an average of the pixelvalues of the corresponding pixels as a pixel value of a correspondingpixel in the authentication image.

According to the first aspect, an average of pixel values of pixelscorresponding to each other between the image in the third polarizationdirection and the image in the fourth polarization direction can be avalue obtained by reducing the influence of the image due to thebirefringence of the cornea. By determining such a pixel value as apixel value of a corresponding pixel in the authentication image, theimage due to the birefringence of the cornea can be effectively removedin the authentication image.

An image synthesizing apparatus according to a second aspect of thepresent disclosure includes: an illuminating device that outputslinearly polarized light having a first polarization direction andlinearly polarized light having a second polarization direction; acamera that captures an image in a third polarization directionincluding a plurality of pixels and an image in a fourth polarizationdirection including a plurality of pixels; and a control circuit thatsynthesizes, on a pixel-by-pixel basis, the image in the thirdpolarization direction and the image in the fourth polarizationdirection into an authentication image for iris authentication, whereinthe first polarization direction and the second polarization directionare different from each other, the third polarization direction and thefourth polarization direction are different from each other, and thecamera acquires the image in the third polarization direction using thelinearly polarized light in the first polarization direction and thelinearly polarized light in the second polarization direction andacquires the image in the fourth polarization direction using thelinearly polarized light in the first polarization direction and thelinearly polarized light in the second polarization direction.

According to the second aspect, since the image in the thirdpolarization direction and the image in the fourth polarizationdirection are respectively images acquired using two linearly polarizedlights in the different polarization direction, occurrence of the imagedue to the birefringence of the cornea is prevented. Further, in theimage in the third polarization direction and the image in the fourthpolarization direction in the different polarization directions, evenwhen images of the specular reflection of the cornea appear, the imagescan appear in different positions. Accordingly, in the authenticationimage obtained by combining the image in the third polarizationdirection and the image in the fourth polarization direction, the imageof the specular reflection of the cornea and the image due to thebirefringence of the cornea are reduced. Therefore, an iris region ofthe authentication image can be an image suitable for authentication.For example, the first polarization direction of the linearly polarizedlight can be set to 0 degree and the second polarization direction ofthe linearly polarized light can be set to 90 degrees. The thirdpolarization direction of the image can be set to 0 degree and thefourth polarization direction of the image can be set to 90 degrees.

According to the second aspect of the present disclosure, it is possiblethat the first polarization direction is different from the secondpolarization direction by 90 degrees, that the third polarizationdirection is a linear direction different from the first polarizationdirection by 90 degrees, and that the fourth polarization direction is alinear direction different from the second polarization direction by 90degrees.

According to the second aspect, it is possible to reduce superimpositionof a region where the image of the specular reflection of the cornea inthe image in the third polarization direction can appear and a regionwhere the image of the specular reflection of the cornea in the image inthe fourth polarization direction can appear. Accordingly, in theauthentication image, a removal rate of the image of the specularreflection of the cornea is improved.

According to the second aspect of the present disclosure, it is possiblethat the illuminating device includes: at least one light source; afirst polarizing plate having the first polarization direction andlocated in front of the light source; and a second polarizing platehaving the second polarization direction and located in front of thelight source, that the light source outputs the linearly polarized lighthaving the first polarization direction via the first polarizing plate,and that the light source outputs the linearly polarized light havingthe second polarization direction via the second polarizing plate.

According to the second aspect, the linearly polarized light having thefirst polarization direction and the linearly polarized light having thesecond polarization direction are irradiated together by lighting thelight source. It is easy to control the irradiation of the linearlypolarized light having the first polarization direction and the linearlypolarized light having the second polarization direction.

According to the second aspect of the present disclosure, it is possiblethat the image synthesizing apparatus further includes a diffusingplate, wherein the diffusing plate is disposed in order of theilluminating device, the diffusing plate, and the first polarizing plateand in order of the illuminating device, the diffusing plate, and thesecond polarizing plate, and that when viewed along an optical axis ofthe illuminating device, the first polarizing plate and the secondpolarizing plate each have a size equal to or larger than a size of thediffusing plate, and the diffusing plate has a size equal to or largerthan a size of the illuminating device.

According to the second aspect, the linearly polarized light diffused bythe diffusing plate and thereafter transmitted through the firstpolarizing plate and the second polarizing plate can reduce luminance ofthe image of the specular reflection on the eyeglass or the cornea.Further, even when an extinction coefficient of the polarizing plate islow, it is possible to realize removal of the image of the specularreflection of the linearly polarized light. Since the first polarizingplate and the second polarizing plate are larger than the diffusingplate, the entire illumination light diffused by the diffusing plate canbe made incident on the first polarizing plate or the second polarizingplate. Accordingly, the illumination light diffused by the diffusingplate is prevented from irradiating an object without receivingpolarization by both of the first polarizing plate and the secondpolarizing plate.

According to the second aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the third polarization direction and the image inthe fourth polarization direction and determines a smaller pixel valueof the pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.

According to the second aspect, a pixel value of the image of thespecular reflection of the cornea is large in each of the image in thethird polarization direction and the image in the fourth polarizationdirection. A smaller pixel value among pixel values of pixelscorresponding to each other between the image in the third polarizationdirection and the image in the fourth polarization direction is highlylikely not to be a pixel value of an image of the specular reflection ofthe cornea. By determining such a pixel value as a pixel value of acorresponding pixel in the authentication image, the image of thespecular reflection of the cornea can be effectively removed in theauthentication image.

According to the second aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the third polarization direction and the image inthe fourth polarization direction and determines an average of the pixelvalues of the corresponding pixels as a pixel value of a correspondingpixel in the authentication image.

According to the second aspect, an average of pixel values of pixelscorresponding to each other between the image in the third polarizationdirection and the image in the fourth polarization direction can be avalue obtained by reducing the influence of the image of the specularreflection of the cornea. By determining such a pixel value as a pixelvalue of a corresponding pixel in the authentication image, the image ofthe specular reflection of the cornea can be effectively removed in theauthentication image.

An image synthesizing apparatus according to a third aspect of thepresent disclosure includes: an illuminating device that outputs rightcircularly polarized light and left circularly polarized light; a camerathat captures an image in a right polarization direction including aplurality of pixels and an image in a left polarization directionincluding a plurality of pixels; and a control circuit that synthesizes,on a pixel-by-pixel basis, the image in the right polarization directionand the image in the left polarization direction into an authenticationimage for iris authentication, wherein the camera acquires the image inthe right polarization direction using the right circularly polarizedlight and the left circularly polarized light and acquires the image inthe left polarization direction using the right circularly polarizedlight and the left circularly polarized light.

According to the third aspect, the image of the right circularlypolarized light and the image of the left circularly polarized light arerespectively images acquired by using the right circularly polarizedlight and the left circularly polarized light. Therefore, occurrence ofthe image due to the birefringence of the cornea is prevented. Further,in the image of the right circularly polarized light and the image ofthe left circularly polarized light, even when images of specularreflection of the cornea appear, the images can appear in differentpositions. Accordingly, in the authentication image obtained bycombining the image of the right circularly polarized light and theimage of the left circularly polarized light, the image of the specularreflection of the cornea and the image due to the birefringence of thecornea are reduced. Therefore, an iris region of the authenticationimage can be an image suitable for authentication.

According to the third aspect of the present disclosure, it is possiblethat the illuminating device includes: at least one light source; aright polarizing plate having the right polarization direction andlocated in front of the light source; and a left polarizing plate havingthe left polarization direction and located in front of the lightsource, that the light source outputs the right circularly polarizedlight via the right polarizing plate, and that the light source outputsthe left circularly polarized light via the left polarizing plate.

According to the third aspect, the right circularly polarized light andthe left circularly polarized light are irradiated together by lightingthe light source. It is easy to control the irradiation of the rightcircularly polarized light and the left circularly polarized light.

According to the third aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the right polarization direction and the image inthe left polarization direction and determines a smaller pixel value ofthe pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.

According to the third aspect, a pixel value of the image of thespecular reflection of the cornea is large in each of the image of theright circularly polarized light and the image of the left circularlypolarized light. A smaller pixel value of pixel values of pixelscorresponding to each other between the image of the right circularlypolarized light and the image of the left circularly polarized light ishighly likely not to be a pixel value of the image of the specularreflection of the cornea. By determining such a pixel value as a pixelvalue of a corresponding pixel in the authentication image, the image ofthe specular reflection of the cornea can be effectively removed in theauthentication image.

According to the third aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the right polarization direction and the image inthe left polarization direction and determines an average of the pixelvalues of the corresponding pixels as a pixel value of a correspondingpixel in the authentication image.

According to the third aspect, an average of pixel values of pixelscorresponding to each other between the image of the right circularlypolarized light and the image of the left circularly polarized light canbe a value obtained by reducing the influence of the image of thespecular reflection of the cornea. By determining such a pixel value asa pixel value of a corresponding pixel in the authentication image, theimage of the specular reflection of the cornea can be effectivelyremoved in the authentication image.

An image synthesizing apparatus according to a fourth aspect of thepresent disclosure includes: an illuminating device that simultaneouslyoutputs first linearly polarized light having a first polarizationdirection, second linearly polarized light having a second polarizationdirection, third linearly polarized light having a third polarizationdirection, and fourth linearly polarized light having a fourthpolarization direction; a camera that captures a fifth image in thefirst polarization direction including a plurality of pixels, a sixthimage in the second polarization direction including a plurality ofpixels, a seventh image in the third polarization direction including aplurality of pixels, and an eighth image in the fourth polarizationdirection including a plurality of pixels; and a control circuit thatsynthesizes, on a pixel-by-pixel basis, the fifth image, the sixthimage, the seventh image, and the eighth image into an authenticationimage for iris authentication, wherein the first polarization direction,the second polarization direction, the third polarization direction, andthe fourth polarization direction are different from one another by 45degrees, and the camera acquires the fifth image, the sixth image, theseventh image, and the eighth image respectively using the firstlinearly polarized light, the second linearly polarized light, the thirdlinearly polarized light, and the fourth linearly polarized light.

According to the fourth aspect, the fifth to the eighth images arerespectively images acquired using the linearly polarized lights havingthe first to fourth polarization directions. Therefore, occurrence ofthe image due to the birefringence of the cornea is prevented. Further,in the fifth to the eighth images, even if images of the specularreflection of the cornea appear, the images appear in differentpositions. Accordingly, in the authentication image obtained bycombining the fifth to the eighth images, the image of the specularreflection of the cornea and the image due to the birefringence of thecornea are reduced. In particular, when the number of images to becombined increases, a probability of appearance of images of thespecular reflection of the cornea in the same positions in all theimages decreases. Therefore, an iris region of the authentication imagecan be an image suitable for authentication. For example, the firstpolarization direction, the second polarization direction, the thirdpolarization direction, and the fourth polarization direction of thelinearly polarized light can be respectively set to 0 degree, 45degrees, 90 degrees, and 135 degrees. The first polarization direction,the second polarization direction, the third polarization direction, andthe fourth polarization direction of the image can be respectively setto 0 degree, 45 degrees, 90 degrees, and 135 degrees.

According to the fourth aspect of the present disclosure, it is possiblethat the illuminating device includes: at least one light source; afirst polarizing plate having the first polarization direction andlocated in front of the light source; a second polarizing plate havingthe second polarization direction and located in front of the lightsource; a third polarizing plate having the third polarization directionand located in front of the light source; and a fourth polarizing platehaving the fourth polarization direction and located in front of thelight source, that the light source outputs linearly polarized lighthaving the first polarization direction via the first polarizing plate,the light source outputs linearly polarized light having the secondpolarization direction via the second polarizing plate, that the lightsource outputs linearly polarized light having the third polarizationdirection via the third polarizing plate, and that the light sourceoutputs linearly polarized light having the fourth polarizationdirection via the fourth polarizing plate.

According to the fourth aspect, the linearly polarized lights having thefirst to fourth polarization directions are irradiated together bylighting the light source. It is easy to control the irradiation of thelinearly polarized lights having the first to fourth polarizationdirections.

According to the fourth aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to one anotheramong the fifth image, the sixth image, the seventh image, and theeighth image and determines a smallest pixel value among the pixelvalues of the corresponding pixels as a pixel value of a correspondingpixel in the authentication image.

According to the fourth aspect, a pixel value of the image of thespecular reflection of the cornea is large in each of the fifth image,the sixth image, the seventh image, and the eighth image. A smallestpixel value among pixel values of pixels corresponding to one anotheramong the fifth image, the sixth image, the seventh image, and theeighth image is highly likely not to be a pixel value of the image ofthe specular reflection of the cornea. By determining such a pixel valueas pixel values of the pixels of the authentication image, the image ofthe specular reflection of the cornea can be effectively removed in theauthentication image.

According to the fourth aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to one anotheramong the fifth image, the sixth image, the seventh image, and theeighth image and determines an average of the pixel values of thecorresponding pixels as a pixel value of a corresponding pixel in theauthentication image.

According to the fourth aspect, an average of pixel values among pixelscorresponding to one another among the fifth image, the sixth image, theseventh image, and the eighth image can be a value obtained by reducingthe influence of the image of the specular reflection of the cornea. Bydetermining such a pixel value as pixel values of the pixels of theauthentication image, the image of the specular reflection of the corneacan be effectively removed in the authentication image.

An image synthesizing apparatus according to a fifth aspect of thepresent disclosure includes: an illuminating device that outputs firstlinearly polarized light having a first polarization direction, secondlinearly polarized light having a second polarization direction, andthird linearly polarized light having a third polarization direction; acamera that images a fourth image in a fourth polarization directionincluding a plurality of pixels, a fifth image in a fifth polarizationdirection including a plurality of pixels, and a sixth image in a sixthpolarization direction including a plurality of pixels; and a controlcircuit that synthesizes, on a pixel-by-pixel basis, the fourth image,the fifth image, and the sixth image into an authentication image foriris authentication. The first polarization direction, the secondpolarization direction, and the third polarization direction aredifferent from one another. The fourth polarization direction, the fifthpolarization direction, and the sixth polarization direction aredifferent from one another. The camera acquires the fourth image, thefifth image, and the sixth image respectively using the first linearlypolarized light, the second linearly polarized light, and the thirdlinearly polarized light.

According to the fifth aspect, the fourth to sixth images are imagesrespectively acquired using the linearly polarized lights having thefirst to third polarization directions. Therefore, occurrence of theimage due to the birefringence of the cornea is prevented. Further, inthe fourth to sixth images, even when images of the specular reflectionof the cornea appear, the images can appear in different positions.Accordingly, in the authentication image obtained by combining thefourth to sixth images, the image of the specular reflection of thecornea and the image due to the birefringence of the cornea are reduced.In particular, when the number of images to be combined increases, aprobability of appearance of images of the specular reflection of thecornea in the same positions in all the images decreases. Therefore, aniris region of the authentication image can be an image suitable forauthentication. For example, the first polarization direction, thesecond polarization direction, and the third polarization direction ofthe linearly polarized light can be respectively set to any one of 0degree, 45 degrees, 90 degrees, and 135 degrees. The fourth polarizationdirection, the fifth polarization direction, and the sixth polarizationdirection of the image can be respectively set to any one of 0 degree,45 degrees, 90 degrees, and 135 degrees.

An iris authentication system according to an aspect of the presentdisclosure includes: the image synthesizing apparatus according to theabove aspect and an iris authentication circuit, wherein the irisauthentication circuit acquires iris authentication information in whicha plurality of user identifications (IDs) and a plurality of referenceimages are associated with each other and identifies a user ID withreference to the authentication image and the iris authenticationinformation. According to the aspect, the same effect as the effect ofthe image synthesizing apparatus explained above can be obtained.Further, it is possible to highly accurately identify a user by usingthe authentication image of the image synthesizing apparatus.

An image synthesizing method according to a first aspect of the presentdisclosure includes: sequentially outputting first linearly polarizedlight having a first polarization direction and second linearlypolarized light having a second polarization direction; when the firstlinearly polarized light is output, capturing an image to acquire athird image in a third polarization direction including a plurality ofpixels; when the second linearly polarized light is output, capturing animage to acquire a fourth image in a fourth polarization directionincluding a plurality of pixels; and synthesizing, on a pixel-by-pixelbasis, the third image and the fourth image into an authentication imagefor iris authentication. The first polarization direction, the secondpolarization direction, the third polarization direction, and the fourthpolarization direction are different from one another. At least one ofthe sequential outputting, the capturing of the image to acquire thethird image, the capturing of the image to acquire to the fourth image,and synthesizing is executed by at least one control circuit. Accordingto the aspect, the same effects as the effect of the image synthesizingapparatus according to the first aspect of the present disclosure can beobtained.

According to the first aspect, it is possible that the firstpolarization direction is different from the second polarizationdirection by 45 degrees, that the third polarization direction is alinear direction different from the first polarization direction by 90degrees, and that the fourth polarization direction is a lineardirection different from the second polarization direction by 90degrees.

According to the first aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and a larger pixel value of the pixel values of the corresponding pixelsis determined as a pixel value of a corresponding pixel in theauthentication image.

According to the first aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and an average of the pixel values of the corresponding pixels isdetermined as a pixel value of a corresponding pixel in theauthentication image.

An image synthesizing method according to a second aspect of the presentdisclosure includes: outputting first linearly polarized light having afirst polarization direction and second linearly polarized light havinga second polarization direction together; capturing an image when thefirst linearly polarized light and the second linearly polarized lightare output; acquiring, from the image, a third image in a thirdpolarization direction including a plurality of pixels and a fourthimage in a fourth polarization direction including a plurality ofpixels; and synthesizing, on a pixel-by-pixel basis, the third image andthe fourth image into an authentication image for iris authentication.The first polarization direction and the second polarization directionare different from each other, the third polarization direction and thefourth polarization direction are different from each other. At leastone of the outputting, the capturing the image, the acquiring, andsynthesizing is executed by at least one control circuit. According tothe above aspect, the same effect as the effect of the imagesynthesizing apparatus according to the second aspect of the presentdisclosure can be obtained.

According to the second aspect, it is possible that the firstpolarization direction is different from the second polarizationdirection by 90 degrees, that the third polarization direction is alinear direction different from the first polarization direction by 90degrees, and that the fourth polarization direction is a lineardirection different from the second polarization direction by 90degrees.

According to the second aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and a smaller pixel value of the pixel values of the correspondingpixels is determined as a pixel value of a corresponding pixel in theauthentication image.

According to the second aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and an average of the pixel values of the corresponding pixels isdetermined as a pixel value of a corresponding pixel in theauthentication image.

An image synthesizing method according to a third aspect of the presentdisclosure includes: outputting right circularly polarized light andleft circularly polarized light together; capturing an image when theright circularly polarized light and the left circularly polarized lightare output; acquiring, from the image, an image in a right polarizationdirection including a plurality of pixels and an image in a leftpolarization direction including a plurality of pixels; andsynthesizing, on a pixel-by-pixel basis, the image in the rightpolarization direction and the image in the left polarization directioninto an authentication image for iris authentication. At least one ofthe outputting, the capturing, the acquiring, and synthesizing isexecuted by at least one control circuit. According to the above aspect,the same effect as the effect of the image synthesizing apparatusaccording to the third aspect of the present disclosure can be obtained.

According to the third aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the image in the right polarizationdirection and the image in the left polarization direction, and asmaller pixel value of the pixel values of the corresponding pixels isdetermined as a pixel value of a corresponding pixel in theauthentication image.

According to the third aspect, it is possible that in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the image in the right polarizationdirection and the image in the left polarization direction, and anaverage of the pixel values of the corresponding pixels is determined asa pixel value of a corresponding pixel in the authentication image.

An image synthesizing method according to a fourth aspect of the presentdisclosure includes: simultaneously outputting first linearly polarizedlight having a first polarization direction, second linearly polarizedlight having a second polarization direction, third linearly polarizedlight having a third polarization direction, and fourth linearlypolarized light having a fourth polarization direction; capturing animage when the first linearly polarized light, the second linearlypolarized light, the third linearly polarized light, and the fourthlinearly polarized light are output; acquiring, from the image, a fifthimage in the first polarization direction including a plurality ofpixels, a sixth image in the second polarization direction including aplurality of pixels, a seventh image in the third polarization directionincluding a plurality of pixels, and an eighth image in the fourthpolarization direction including a plurality of pixels; synthesizing, ona pixel-by-pixel basis, the fifth image, the sixth image, the seventhimage, and the eighth image into an authentication image for irisauthentication. The first polarization direction, the secondpolarization direction, the third polarization direction, the fourthpolarization direction are different from each other by 45 degrees. Atleast one of the simultaneously outputting, the capturing, theacquiring, and synthesizing is executed by at least one control circuit.According to the above aspect, the same effect as the effect of theimage synthesizing apparatus according to the fourth aspect of thepresent disclosure can be obtained.

According to the fourth aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, pixel values ofpixels corresponding to one another are compared among the fifth image,the sixth image, the seventh image, and the eighth image, and a smallestpixel value among the pixel values of the corresponding pixels isdetermined as a pixel value of a corresponding pixel in theauthentication image.

According to the fourth aspect of the present disclosure, it is possiblethat in the synthesizing of the authentication image, pixel values ofpixels corresponding to one another are compared among the fifth image,the sixth image, the seventh image, and the eighth image, and an averageof the pixel values of the corresponding pixels is determined as a pixelvalue of a corresponding pixel in the authentication image.

An image synthesizing method according to a fifth aspect of the presentdisclosure includes: outputting first linearly polarized light having afirst polarization direction and second linearly polarized light havinga second polarization direction together; capturing an image when thefirst linearly polarized light and the second linearly polarized lightare output; acquiring, from the image, a third image in a thirdpolarization direction including a plurality of pixels and a fourthimage in a fourth polarization direction including a plurality ofpixels; and synthesizing, on a pixel-by-pixel basis, the third image andthe fourth image into an authentication image for iris authentication.The first polarization direction and the second polarization directionare different from each other, the third polarization direction and thefourth polarization direction are different from each other. At leastone of the outputting, the capturing the image, the acquiring, andsynthesizing is executed by at least one control circuit. According tothe above aspect, the same effect as the effect of the imagesynthesizing apparatus according to the fifth aspect of the presentdisclosure can be obtained.

An iris authenticating method according to an aspect of the presentdisclosure includes: acquiring the authentication image generated by theimage synthesizing method; acquiring iris authentication information inwhich a plurality of user identifications (IDs) and a plurality ofreference images are associated; and identifying a user ID withreference to the authentication image and the iris authenticationinformation. At least one of the kinds of processing is executed by atleast one control circuit. According to the aspect, the same effect asthe effect of the image combining method explained above can beobtained. Further, it is possible to highly accurately identify a userby using the authentication image generated by the image synthesizingmethod.

The comprehensive and specific forms explained above may be realized asa system, an apparatus, a method, an integrated circuit, a computerprogram, or a computer-readable recording medium such as a recordingdisk or may be realized as any combination of the system, the apparatus,the method, the integrated circuit, the computer program, and therecording medium. The computer-readable recording medium includes anonvolatile recording medium such as a CD-ROM. The apparatus may beconfigured by one or more apparatuses. When the apparatus is configuredby two or more apparatuses, the two or more apparatuses may be disposedin one machine or may be separately disposed in separated two or moremachines. In this specification and the claims, “apparatus” not only canmean one apparatus but also can mean a system including a plurality ofapparatuses.

An image synthesizing apparatus and the like according to the presentdisclosure is specifically explained below with reference to thedrawings. All of the embodiments explained below indicate comprehensiveor specific examples. Numerical values, shapes, components, dispositionpositions and connection forms of the components, steps, the order ofthe steps, and the like described in the following embodiments areexamples and are not meant to limit the present disclosure. Among thecomponents in the following embodiments, components not described in anindependent claim indicating a highest-order concept are explained asoptional components. The figures are schematic figures and are notalways strictly illustrated. Further, in the figures, substantially thesame components are denoted by the same reference numerals and signs.Redundant explanation of the components is sometimes omitted orsimplified.

First Embodiment

Image synthesizing apparatus 100 and iris authentication system 1including image synthesizing apparatus 100 according to a firstembodiment are explained. In the embodiment explained below, imagesynthesizing apparatus 100 generates a synthesized image for irisauthentication by combining captured images of an eyeball on whichpolarized lights in different polarization directions are irradiated.Iris authentication system 1 authenticates an iris in the synthesizedimage for the iris authentication by collating the synthesized image forthe iris authentication with an iris image of a database.

[1-1. Configuration of Iris Authentication System 1]

The configuration of iris authentication system 1 according to the firstembodiment is explained. FIG. 1 is a block diagram showing an example ofa functional configuration of iris authentication system 1 according tothe first embodiment. FIG. 2 is a schematic diagram showing an exampleof a flow of processing by components of iris authentication system 1according to the first embodiment. As shown in FIG. 1, irisauthentication system 1 includes image synthesizing apparatus 100, irisauthenticator 110, iris authentication pattern database (hereinafterreferred to as “iris authentication pattern DB” as well) 120, and outputsection 130. Image synthesizing apparatus 100 includes processor 10,illuminating device 20, and camera 30. Processor 10 includessynchronizer 11, storage 12, pixel selector 13, and polarized imagesynthesizer 14.

[Image Synthesizing Apparatus 100]

(Illuminating Device 20)

As illustrated in FIGS. 1 and 2, illuminating device 20 of imagesynthesizing apparatus 100 irradiates polarized light on an object ofcamera 30. In this embodiment, the object is eyeball E of a person.Illuminating device 20 irradiates lights in two different polarizationdirections. Illuminating device 20 includes illuminator 20 a andpolarizer 20 b. Illuminator 20 a emits light. Polarizer 20 b convertsthe emitted light of illuminator 20 a into linearly polarized light. Anexample of the irradiation light of illuminator 20 a is infrared lightor visible light. An example of illuminator 20 a is a luminaire, anillumination circuit, a light emitting element such as an LED (LightEmitting Diode) element, a bulb such as an infrared bulb, or a laserbeam emitting device.

FIG. 3 is a schematic front view of illuminating device 20 according tothe first embodiment. In FIG. 3 and the other figures, a front view anda plan view of the illuminating device are views of the illuminatingdevice viewed while being opposed to an irradiating direction ofillumination light and are views of the illuminating device viewed froman object of the camera. In the front view and the plan view of theilluminating device, straight line arrows and circular arrows indicatingpolarization directions, which are directions of polarizationtransmission axes explained below, are described. However, thedirections of these arrows indicate directions at the time when theobject is viewed from the camera, that is, when the object is viewedfrom the illuminating device.

As shown in FIGS. 2 and 3, illuminator 20 a includes a plurality offirst light sources 20 aa and a plurality of second light sources 20 abdisposed in a ring shape around opening 20 c. In this embodiment, firstlight sources 20 aa and second light sources 20 ab are alternatelydisposed along the circumference of opening 20 c. An example of firstlight sources 20 aa and second light sources 20 ab is a light emittingelement such as an LED element, a bulb such as an infrared bulb, or alaser light source. Illuminator 20 a is configured to cause theplurality of first light sources 20 aa to simultaneously emit lights tothereby emit ring-like illumination light. Illuminator 20 a isconfigured to cause the plurality of second light sources 20 ab tosimultaneously emit lights to thereby emit ring-like illumination light.First light sources 20 aa and second light sources 20 ab are configuredto be lit independently from each other. Such illuminator 20 a is a ringlight having a two-channel configuration.

Polarizer 20 b is a polarizing filter disposed between illuminator 20 aand the object. An example of polarizer 20 b is a polarizing plate or apolarizing film. Polarizer 20 b includes a plurality of first polarizingfilters 20 ba and a plurality of second polarizing filters 20 bbdisposed in a ring shape around opening 20 c. An example of firstpolarizing filters 20 ba and second polarizing filters 20 bb is apolarizing plate or a polarizing film. In this embodiment, firstpolarizing filters 20 ba and second polarizing filters 20 bb arealternately disposed along the circumference of opening 20 c.

First polarizing filters 20 ba have polarization transmission axes in adirection of 90° (90 degrees) at an angle in an image plane in a cameracoordinate system of camera 30, that is, an azimuth angle. Firstpolarizing filters 20 ba are disposed between first light sources 20 aaand the object and changes emitted lights of first light sources 20 aainto linearly polarized lights having an azimuth angle of 90°. In theimage plane in the camera coordinate system, the azimuth angle increasesin a clockwise, that is, right direction. The azimuth angle in thehorizontal direction is 0°. The azimuth angle in the vertical directionis 90°. The azimuth angle indicates a direction from the camera towardthe object. The same applies to directions of polarization transmissionaxes of right and left circularly polarized lights. The direction of theright polarization transmission axis is the clockwise direction in theimage plane of the camera coordinate system. The direction of the leftpolarization transmission axis is the counterclockwise direction. Whenviewed from illuminating device 20 toward camera 30, the directions ofthe left and the right of the arrows shown in FIG. 3 are reversed. Theright and left rotating directions are also reversed. In thisspecification and the claims, the azimuth angle of the polarizationtransmission axis is simply represented as “polarization direction”.

Second polarizing filters 20 bb have the polarization transmission axesin the direction of 135° as the azimuth angle in the image plane in thecamera coordinate system of camera 30. The azimuth angles of thepolarization transmission axes of first polarizing filters 20 ba andsecond polarizing filters 20 bb are different from each other by 45°.Second polarizing filters 20 bb are disposed between second lightsources 20 ab and the object and changes emitted lights of second lightsources 20 ab to linearly polarized lights at the azimuth angle of 135°.First polarizing filters 20 ba and second polarizing filters 20 bb arerespectively disposed to correspond to first light sources 20 aa andsecond light sources 20 ab.

Illuminating device 20 causes first light sources 20 aa and second lightsources 20 ab to temporally sequentially emit lights to therebytemporally sequentially irradiate, on eyeball E of an authenticationtarget person, ring-shaped illumination lights L, which are linearlypolarized lights in polarization directions of 90° and 135° differentfrom each other by 45°. Return lights reflected in cornea and irisportions of eyeball E pass through opening 20 c in the center ofdoughnut-type illuminating device 20 and are made incident on camera 30.In this embodiment, band-pass filter 40 is disposed between illuminatingdevice 20 and camera 30. However, band-pass filter 40 is not essential.If band-pass filter 40 is disposed, the return lights from eyeball Epass through band-pass filter 40 and thereafter are made incident oncamera 30. The authentication target person may be a specific personpresent within the field of view of camera 30 or may be any person.

(Camera 30)

As illustrated in FIGS. 1 and 2, camera 30 of image synthesizingapparatus 100 captures a digital image. Camera 30 may capture both of astill image and a moving image. Camera 30 includes polarization imagingelement 30 a and objective lens 30 b. Objective lens 30 b receives thereturn lights reflected on eyeball E and condenses the return lights onpolarization imaging element 30 a. Polarization imaging element 30 agenerates an image signal from an image which is formed on polarizationimaging element 30 a by objective lens 30 b.

FIG. 4A is a plan view schematically showing the configuration ofpolarization imaging element 30 a of camera 30 according to the firstembodiment. FIG. 4B is a plan view showing one unit of a group ofpolarizing filters in mosaic polarizing filter 30 ab shown in FIG. 4A.In FIGS. 4A and 4B and the other figures, a plan view of thepolarization imaging element and the group of the polarizing filters isa view at the time when the object is viewed from the camera. In theseplan views, straight line arrows and circular arrows indicatingpolarization directions, which are directions of polarizationtransmission axes explained below, are described. However, thedirections of these arrows indicate directions at the time when theobject is viewed from the camera.

As shown in FIG. 4A, polarization imaging element 30 a includes imagingelement 30 aa including light receiving elements and mosaic polarizingfilter 30 ab disposed on imaging element 30 aa. An example of mosaicpolarizing filter 30 ab is a mosaic polarizing plate or a polarizingfilm. Imaging element 30 aa includes a plurality of light receivingelements respectively corresponding to pixels of an image to be formed.One light receiving element generates a pixel value of one pixel. Thelight receiving element outputs a signal indicating characteristics oflight such as luminance of received light to storage 12 of processor 10.An example of the pixel value is luminance.

An example of imaging element 30 aa is an image sensor such as a CMOS(Complementary Metal Oxide Semiconductor) image sensor or a CCD(Charge-Coupled Device) image sensor. Mosaic polarizing filter 30 ab isdisposed between objective lens 30 b and imaging element 30 aa andpolarizes light made incident on polarization imaging element 30 a andoutputs the light to imaging element 30 aa. Mosaic polarizing filter 30ab is disposed to cover entire imaging element 30 aa. An example ofmosaic polarizing filter 30 ab is a wire grid. Light collected inpolarization imaging element 30 a from objective lens 30 b passesthrough mosaic polarizing filter 30 ab and is thereafter made incidenton imaging element 30 aa.

As shown in FIGS. 4A and 4B, mosaic polarizing filter 30 ab isconfigured by a planarly disposed plurality of polarizing filters. Anexample of the polarizing filters is a polarizing plate or a polarizingfilm. One polarizing filter is disposed with respect to each of thelight receiving elements of imaging element 30 aa. Such a plurality ofpolarizing filters are arrayed in a lattice shape in the same manner asthe light receiving elements. The plurality of polarizing filters areconfigured by a plurality of first linear polarizing filters 30 aca anda plurality of second linear polarizing filters 30 acb. In the imageplane in the camera coordinate system of camera 30, an azimuth angle,which is an angle of polarization transmission axes, of first linearpolarizing filters 30 aca is 0° and an azimuth angle of polarizationtransmission axes of second linear polarizing filters 30 acb is 450. Anaxis of the azimuth angle 0° is a reference axis in the horizontaldirection of camera 30 and imaging element 30 aa. The plurality of firstlinear polarizing filters 30 aca and the plurality of second linearpolarizing filters 30 acb and the plurality of light receiving elementsof imaging element 30 aa are arranged in a lattice shape in thedirection of the azimuth angle 0° and the direction of the azimuth angle90°. The azimuth angle 0° of the polarization transmission axes of firstlinear polarizing filters 30 aca is perpendicular to the azimuth angle90° of the polarization transmission axes of first polarizing filters 20ba of illuminating device 20. The azimuth angle 45° of the polarizationtransmission axes of second linear polarizing filters 30 acb isperpendicular to the azimuth angle 135° of the polarization transmissionaxes of second polarizing filters 20 bb of illuminating device 20. Thatis, the azimuth angles of the polarization transmission axes of firstlinear polarizing filters 30 aca and second linear polarizing filters 30acb are set to be perpendicular to the azimuth angles of thepolarization transmission axes of first polarizing filters 20 ba andsecond polarizing filters 20 bb of illuminating device 20.

Two first linear polarizing filters 30 aca and two second linearpolarizing filters 30 acb are disposed adjacent to each other centeringon one point P. First linear polarizing filters 30 aca and second linearpolarizing filters 30 acb are alternately disposed in a rotatingdirection centering on the point P. Such two first linear polarizingfilters 30 aca and two second linear polarizing filters 30 acb form onepolarizing filter group 30 ac. In one polarizing filter group 30 ac, twofirst linear polarizing filters 30 aca and two linear polarizing filters30 acb are disposed in a square shape in an array of 2×2, that is,disposed in a lattice shape.

In mosaic polarizing filter 30 ab, a plurality of polarizing filtergroups 30 ac are arrayed in a lattice shape, that is, a mosaic shape.The plurality of first linear polarizing filters 30 aca and theplurality of second linear polarizing filters 30 acb are arrayed in alattice shape, that is, a mosaic shape. First linear polarizing filters30 aca and the light receiving elements of imaging element 30 aa form amicro polarized pixel that polarizes incident light in the direction of0° and receives the incident light. Second linear polarizing filters 30acb and the light receiving elements of imaging element 30 aa form amicro polarized pixel that polarizes incident light in the direction of45° and receives the incident light. One image acquired by suchpolarization imaging element 30 a includes polarized pixels, which arepixels polarized in the directions of 0° and 45°. Mosaic polarizingfilter 30 ab only has to include polarizing filters having two kinds ofpolarization transmission axes perpendicular to the azimuth angles ofthe polarization transmission axes of first polarizing filters 20 ba andsecond polarizing filters 20 bb of illuminating device 20. Therefore,the mosaic polarizing filter may be configured by four kinds ofpolarizing filters formed by more general polarization transmission axesof 0°, 45°, 90°, and 135°. In this case, in the polarization imagingelement, a polarized pixel including a pertinent polarizationtransmission axis may be selected and used.

In camera 30 explained above, light reflected on eyeball E is focused onmosaic polarizing filter 30 ab by objective lens 30 b and furtherpolarized by mosaic polarizing filter 30 ab and thereafter received byimaging element 30 aa. Imaging element 30 aa outputs information such asa signal indicating characteristics of the light detected by the lightreceiving elements to storage 12 of processor 10. At this time, imagingelement 30 aa captures an image through exposure on the basis of asignal of synchronizer 11 of processor 10 in each of periods in whichilluminating device 20 alternately lights first light source 20 aa andsecond light source 20 ab. Camera 30 can simultaneously acquire, fromsubstantially the same visual point, polarized images formed by twokinds of polarized pixels via polarizing filters in differentpolarization transmission axis directions of 0° and 45° in respectivelighting periods. By using such polarized images, it is possible toeasily perform image processing in which pixels of these polarizedimages are matched.

(Processor 10)

The components of processor 10 of image synthesizing apparatus 100 areexplained with reference to FIGS. 1 and 2. The components includingsynchronizer 11, pixel selector 13, and polarized image synthesizer 14of processor 10 may be configured by a computer system (not shown inFIGS. 1 and 2) including a processor such as a CPU (Central ProcessingUnit) or a DSP (Digital Signal Processor) and memories such as a RAM(Random Access Memory) and a ROM (Read-Only Memory). Functions of a partor all of the components may be achieved by the CPU or the DSP executingcomputer programs recorded in the ROM using the RAM as a work memory.The functions of a part or all of the components may be achieved by adedicated hardware circuit such as an electronic circuit or anintegrated circuit. The functions of a part or all of the components maybe configured by a combination of the software functions and a hardwarecircuit. The computer programs may be provided as applications throughcommunication via a communication network such as the Internet,communication by a mobile communication standard, or another wirelessnetwork, a wired network, broadcast, or the like. Processor 10 is anexample of a control circuit.

Storage 12 enables storage and extraction of various kinds ofinformation. For example, storage 12 stores a captured image acquired bycamera 30. Storage 12 may store computer programs for causing processor10 and/or camera 30 to operate. These computer programs may be stored innot-shown memories included in processor 10 and camera 30. Storage 12 isrealized by a storage device such as a semiconductor memory such as aROM, a RAM, or a flash memory, a hard disk drive, or an SSD (Solid StateDrive).

Synchronizer 11 controls the operations of illuminating device 20 andcamera 30 to synchronize timing of two kinds of illumination ofilluminating device 20 and timing of imaging of camera 30. Specifically,synchronizer 11 controls lighting and extinction of each of first lightsource 20 aa and second light source 20 ab of illuminating device 20 andtemporally sequentially lights first light source 20 aa and second lightsource 20 ab. Further, synchronizer 11 causes camera 30 to performimaging at least once during the lighting of first light source 20 aaand causes camera 30 to acquire at least one image. Synchronizer 11causes camera 30 to perform imaging at least once during the lighting ofsecond light source 20 ab and causes camera 30 to acquire at least oneimage. Further, synchronizer 11 outputs imaging timing of camera 30during the lighting of first light source 20 aa and imaging timing ofcamera 30 during the lighting of second light source 20 ab to polarizedimage synthesizer 14.

Pixel selector 13 generates two kinds of polarized images by performingre-accumulation processing of pixels acquired via first liner polarizingfilters 30 aca and pixels acquired via second linear polarizing filters30 acb in an image acquired by polarization imaging element 30 a ofcamera 30. A first polarized image of the two kinds of polarized imagesis an image formed by polarized pixels C0, which are pixels acquired viafirst linear polarizing filters 30 aca. A second polarized image is animage formed by polarized pixels C45, which are pixels acquired viasecond linear polarizing filters 30 acb. In the following explanation, apolarized pixel acquired via a linear polarizing filter, a direction ofa polarization transmission axis of which is α°, is represented as“polarized pixel Ca” as well. Pixel selector 13 acquires a capturedimage of camera 30 from storage 12, generates, from the captured image,a polarized image formed by polarized pixels C0 and a polarized imageformed by polarized pixels C45, and outputs the polarized images topolarized image synthesizer 14. When longitudinal and lateral sizes ofthe captured image of polarization imaging element 30 a are respectivelyrepresented as H and W, both the polarized images are reduced imageshaving a longitudinal size of H/2 and a lateral size of W/2. Thepositions of pixels between the polarized images can be regarded as thesame sampling positions with almost no positional deviation.

Polarized image synthesizer 14 associates the imaging timings of camera30 during the lighting of first light source 20 aa and second lightsource 20 ab acquired from synchronizer 11 and the polarized imagesrespectively formed by polarized pixels C0 and polarized pixels C45acquired from pixel selector 13. For example, the captured image ofcamera 30 includes information concerning imaging time. The polarizedimage generated from the captured image includes the same informationconcerning the imaging time. Polarized image synthesizer 14 specifies alight source lit during the imaging of the polarized image byassociating the imaging time of the polarized image and the imagingtimings in the lightings. Polarized image synthesizer 14 synthesizes,into an image, polarized images of two captured images captured duringadjacent two lighting periods of first light source 20 aa and secondlight source 20 ab. Specifically, polarized image synthesizer 14combines polarized image L90C0 formed by polarized pixels C0 of acaptured image captured during a lighting period of first light source20 aa, that is, an illumination period of 90° linearly polarized light(represented as “linearly polarized illumination L90” or “linearlypolarized light L90” as well) and polarized image L135C45 formed bypolarized pixels C45 of a captured image captured during a lightingperiod of second light source 20 ab, that is, during an illuminationperiod of 135° linearly polarized light (represented as “linearlypolarized illumination L135” or “linearly polarized light L135” aswell). Polarized image synthesizer 14 combines the images as explainedabove to thereby generate a synthesized image for authentication forauthenticating an owner of eyeball E. Polarized image synthesizer 14outputs the synthesized image for authentication to iris authenticator110. The two lighting periods corresponding to the two captured imagesdo not have to adjacent to each other.

[Iris Authenticator 110]

Iris authenticator 110 collates information concerning a plurality ofreference images stored in iris authentication pattern DB 120 and asynthesized image for authentication to thereby identify a user ID, thatis, identification information corresponding to the synthesized imagefor authentication. The plurality of reference images are imagesincluding images of eyeballs of people and are associated with user IDsof owners of the eyeballs. The reference images and the user IDs areassociated with each other and stored in iris authentication pattern DB120 as iris authentication information. For example, iris authenticator110 determines a reference image having predetermined or highersimilarity to the synthesized image for authentication out of theplurality of reference images and identifies a user ID associated withthe determined reference image. The plurality of reference images aretypically binary image patterns disclosed in Patent Literature 1. Forexample, similarity between each of the plurality of reference imagesand the synthesized image for authentication is calculated as aninter-signal distance. Details of this processing are referred to inPatent Literature 1. Iris authenticator 110 outputs an identifyingresult of the user ID to output section 130.

Iris authenticator 110 may have any one of the configurationsillustrated concerning the components of processor 10 of imagesynthesizing apparatus 100. Iris authenticator 110 may be disposed in amachine mounted with image synthesizing apparatus 100 or may be disposedin another machine different from the machine. Iris authenticator 110disposed in the other machine may exchange information with imagesynthesizing apparatus 100 via wired communication or wirelesscommunication. The wired communication and the wireless communicationmay be respectively any kinds of communication.

[Iris Authentication Pattern DB 120]

Iris authentication pattern DB 120 stores iris authenticationinformation including reference images and user IDs. Iris authenticationpattern DB 120 may have any one of the configurations illustratedconcerning storage 12. In iris authentication pattern DB 120, onereference image may be stored or a plurality of reference images may bestored for one user ID. The reference image is an image including animage of an eyeball, that is, an iris of a person corresponding to theuser ID. Iris authentication pattern DB 120 may be disposed in a machinemounted with image synthesizing apparatus 100 or may be disposed outsidethe machine. Iris authentication pattern DB 120 disposed outside themachine may exchange information with image synthesizing apparatus 100via wireless communication. In this case, iris authentication pattern DB120 may be disposed in a cloud server and perform the wirelesscommunication with image synthesizing apparatus 100 via a communicationnetwork such as the Internet or may perform any other kind of wirelesscommunication.

[Output Section 130]

Output section 130 outputs an authentication result by irisauthenticator 110 to a machine or the like on the outside of irisauthentication system 1. Output section 130 may visually and/orauditorily output the authentication result to a display device such asa display and a speaker. Output section 130 may output theauthentication result to the external machine via wirelesscommunication. When a user ID corresponding to a synthesized image forauthentication is identified by iris authenticator 110, output section130 may output information concerning the user. When a user ID is notidentified, output section 130 may output information indicating thatauthentication is impossible. Output section 130 may have any one of theconfigurations illustrated concerning the components of processor 10.Output section 130 may be an interface for connection to an externalapparatus or the like. Output section 130 may be disposed in a machinemounted with image synthesizing apparatus 100 or, like irisauthenticator 110, may be disposed in another machine different from themachine.

In this embodiment, the not-shown controller of polarization imagingelement 30 a of camera 30, processor 10, and iris authenticator 110configure processors different from one another. However, all of thecontroller, processor 10, and iris authenticator 110 may configure thesame processor. Any two of the controller, processor 10, and irisauthenticator 110 may configure the same processor.

[1-2. Details of the Processing of Image Synthesizing Apparatus 100]

Details of the processing of image synthesizing apparatus 100 areexplained. First, reflection of light on an eye of a person isexplained. FIG. 5A is a schematic diagram showing a situation in whichenvironment light and illumination light are specularly reflected on acornea or an eyeglass. FIG. 5B is a front view of the eyeglass shown inFIG. 5A. FIG. 5C is a front view of the cornea shown in FIG. 5A. In thefollowing explanation, illuminating device 20 is explained as an IRilluminating device that emits infrared light.

As shown in FIG. 5A, when a face of a person is photographed usingilluminating device 20 indoors or outdoors, illumination light L oflinearly polarized light of illuminating device 20 and environment lightEL, which is external light from an ambient environment such assunlight, are simultaneously directly made incident on eyeball E of theperson. Alternatively, when the person wears eyeglass 140, illuminationlight L and environment light EL are simultaneously directly madeincident on eyeglass 140. Illumination light L has an IR wavelengthregion. Illumination light L and environment light EL are reflected on acornea surface of eyeball E and a glass surface of eyeglass 140 andgenerate a high-luminance reflection spot by strong specular reflectionon the cornea surface and the glass surface. FIG. 5B shows an example ofcaptured images of regions of the eyeglass and the eyeball captured whenthe person wears eyeglass 140 and shows a typical specular reflectionstate on the glass surface of eyeglass 140. In the captured image shownin FIG. 5B, both of specular reflection portion REL by environment lightEL and specular reflection portion RL by illumination light L areobserved. FIG. 5C shows an example of a captured image of the region ofthe eyeball captured when image synthesizing apparatus 100 includesband-pass filter 40 that cuts wavelength regions other than the IRwavelength region of illumination light L. By using such band-passfilter 40, specular reflection portion REL by environment light EL canbe removed.

Functions of band-pass filter 40 are explained. FIG. 6 is a diagramshowing a removal characteristic of specular reflection of environmentlight EL in band-pass filter 40. For example, when a wavelength ofillumination light L is typically set to 940 nm, a narrow-band filterhaving a transmission range near 940 nm is used as optimum band-passfilter 40. Consequently, it is evident that reflected light by lightother than illumination light L of 940 nm can be removed. However,specular reflection portion RL by illumination light L cannot be removedby this method.

For example, FIG. 7A is a diagram showing a generation state of specularreflection of illumination light on a cornea right opposed to camera 30.FIG. 7B is a diagram showing a generation state of specular reflectionof illumination light on an eyeglass and a cornea right opposed tocamera 30. FIG. 7C is a diagram showing a generation state of specularreflection of illumination light on a cornea obliquely facing camera 30.As shown in FIG. 7A, in a naked eye right opposed to camera 30, areflected image of ring-like illumination light is located on the insideon substantially the center of a black pupil. The reflected image of theillumination light is located on the inside on substantially the centerof the black pupil because the position of illuminating device 20, whichis ring illumination, is nearly coaxial with an imaging line of sight ofcamera 30 and because of an effect that a virtual image of the ring-likeillumination light is reduced by a convex curved surface of the cornea.In iris authentication, an image of a pupil portion is not used and animage of an iris portion is used. Therefore, if the reflected image ofthe illumination light is in such a state, there is no problem in theiris authentication.

However, as shown in FIG. 7B, in an eyeball in a worn state of aneyeglass, since a glass surface of the eyeglass is substantially flat,reflected image of ring-like illumination light on the glass surface ofthe eyeglass is extremely large. Therefore, a saturation region ofilluminance of the reflected image of the illumination light hides thepupil and the iris. Since multiple reflection occurs between the glasssurface of the eyeglass and the cornea surface, a large number ofreflected images appear and hide the iris, that is, an iris pattern.

As shown in FIG. 7C, in the case of an oblique naked eye in which theline of sight deviates from an imaging line of sight even if theeyeglass is not worn, a reflected image of the ring-like illuminationlight is located in an iris region. Therefore, a part of an image of theiris, that is, the iris pattern important for authentication lacks.

It has been known that polarization imaging is effective for removal ofthe specular reflection of this type. Therefore, there is a polarizationimaging method for creating, using linearly polarized light of IRillumination light and a polarizing filter set in a camera, anorthogonal polarization state in which polarization directions areorthogonal between the linearly polarized light and the polarizingfilter. However, when an eyeball is imaged in such an orthogonalpolarization state, there is a significant problem in that abirefringent pattern, which is an image due to birefringence of a corneais generated in a captured image, the birefringent pattern issuperimposed on an iris, and accurate iris authentication cannot beperformed.

The birefringent pattern generated in the cornea is explained withreference to FIGS. 8A to 8C. FIG. 8A is a diagram for explaining abirefringence phenomenon in the cornea and is a schematic diagramshowing a situation in which linearly polarized illumination is madeincident and reflected on the cornea. FIG. 8B is a diagram forexplaining the birefringence phenomenon in the cornea and is a schematicfront view showing linearly polarized illumination made incident on thecornea. FIG. 8C is a diagram for explaining the birefringence phenomenonin the cornea and is a schematic front view showing the linearlypolarized illumination reflected on the cornea.

According to Non Patent Literature 1, a cornea of an eyeball hasdifferent refractive indexes respectively in an r direction and a θdirection in a polar coordinate system viewed from the front. The rdirection is a radial direction from the center of the cornea and the θdirection is a rotating direction around the center of the cornea. Aconstituent substance of such a cornea is called birefringent substance.When linearly polarized light is made incident on the birefringentsubstance, the linearly polarized light is transmitted while vibratingin two vibrating directions. Since speeds of light in the two vibratingdirections in a process of the transmission are different, deviationoccurs in phases of the vibration in the two vibrating directions. Thelinearly polarized light sometimes changes to elliptically polarizedlight or circularly polarized light. In this specification and theclaims, the circularly polarized light and the elliptically polarizedlight are collectively described as “circularly polarized light” in somecases or described as “elliptically polarized light” in other cases.Accordingly, both of the “circularly polarized light” and the“elliptically polarized light” can include the circularly polarizedlight and the elliptically polarized light.

As shown in FIG. 8A, when linearly polarized light L0 is made incidenton cornea Ea of eyeball E from right above, that is, the front of corneaEa, a part of linearly polarized light L0 changes to boundary reflectedlight between the air and cornea Ea. The remaining light of linearlypolarized light L0 is transmitted through transparent cornea Ea andaqueous humor Eb, reaches opaque iris Ec, and reflects. The reflectedlight is transmitted through aqueous humor Eb and cornea Ea again,emitted into the air, and reaches camera 30. In a process in which thelinearly polarized light is transmitted through the cornea twice, phasesof the lights in the two vibrating directions of the linearly polarizedlight deviate from each other in the r direction and the 0 direction.The linearly polarized light changes to elliptically polarized light andreaches camera 30. Linearly polarized light L0 is linearly polarizedlight having a vibration surface perpendicular to the paper surface andin a direction of 0° along a horizontal plane including a broken line.

FIG. 8B shows a distribution of an F (Fast) axis and an S (Slow) axis ofbirefringence at the time when cornea Ea is viewed from the front. TheFast axis is called a phase advancing axis as well and is an axis in adirection in which traveling speed of light is high, that is, a phaseadvances. The Slow axis is called a phase delaying axis as well and isan axis in a direction which traveling speed of light is low, that is, aphase is delayed. The Fast axis and the Slow axis are orthogonal. InFIG. 8B, setting is assumed in which an axis in the r direction is theFast axis and an axis in the θ direction is the Slow axis. When FIG. 8Bis considered as an orthogonal coordinate system of an X axis and a Yaxis, only directions of the X axis corresponding to 0=0° and 180° anddirections of the Y axis corresponding to 0=90° and 270° are specialdirections. At this time, one of the F axis and the S axis coincideswith one of the Y axis and the X axis. The other of the F axis and the Saxis coincides with the other of the Y axis and the X axis.

FIG. 8C shows a distribution of a state of polarized light reachingcamera 30 in front of cornea Ea considering the effect of birefringence.FIG. 8C shows how linearly polarized light L0 in polarization direction0° made incident on cornea Ea is affected by the distribution of the Faxis and the S axis. When the directions of the F axis and the S axisare the directions of the X axis and the Y axis, even if a phase shiftoccurs in the light in the two vibrating directions, only a phase shiftoccurs in linearly polarized light L0. Incident linearly polarized lightL0 reflects and returns in the same polarization state. When thedirections of the F axis and the S axis are directions of angles otherthan the X axis and the Y axis, a phase difference occurs between lightsobtained by decomposing linearly polarized light L in the vibratingdirections of the X-axis direction and the Y-axis direction. Therefore,a combination result of these lights forms elliptically polarized light.FIG. 8C shows a state in which, in particular, linearly polarized lightL0 changes to elliptically polarized light when the directions of the Faxis and the S axis form 45 degrees with the X axis and the Y axis. Inthis case, a phase difference between lights in the two vibratingdirections is the largest.

FIG. 9 shows a typical example of a birefringent pattern reflected on acaptured image of the camera by the effect of birefringence of thecornea explained above. Specifically, FIG. 9 schematically shows anexample of a generation state of a black cross pattern in the cornea.When linearly polarized light of illumination light having a lightamount=1 reflected on the eyeball and directly returning as the linearlypolarized light is imaged by camera 30 which is a polarizing camera thatcan observe the polarization state, in an orthogonal polarization statein which polarization directions of the illumination light and thepolarizing filters of camera 30 are orthogonal, ideally, the luminanceof a polarized pixel corresponding to the polarizing filter is 0. In aparallel polarization state in which the polarization directions of theillumination light and the polarizing filter are parallel, ideally, theluminance of the polarized pixel corresponding to the polarizing filteris 1. However, when linearly polarized light having a light amount=1returns as circularly polarized light, the luminance of the polarizedpixel is ½ in both of the parallel and orthogonal states of thepolarization directions of the illumination light and the polarizingfilter. Therefore, when a distribution of a polarization state isdifferent on a two-dimensional plane on which the cornea is viewed fromthe front, in a captured image, the distribution of the polarizationstate appears as a luminance pattern of light and dark.

Specifically, in an orthogonal polarization state in which thepolarization direction of the illumination light is 0° and thepolarization direction of the polarizing filter of camera 30 is 90°(hereinafter represented as “orthogonal polarization state L0C90” aswell), pixels on the X axis and the Y axis show an image of the directlyreturning linearly polarized light. Therefore, ideally, the pixels havethe luminance=0 and are dark. However, pixels on axes in obliquedirections with respect to the X axis and the Y axis show an image ofcircularly polarized light. Therefore, the pixels have the luminance=½and are gray. Consequently, a so-called “black cross pattern” appears asshown in image L0C90 and an image L0C90 image of FIG. 9.

Behaviors of the black cross pattern observed by disposing a simulativecornea, in which a convex lens is used, on a reflecting plate areexplained with reference to FIGS. 10A and 10B. FIGS. 10A and 10B arediagrams showing an example of a pattern for generating a black crossusing the convex lens that changes according to a polarizationdirection. FIG. 10A shows captured image L90C0 of a camera includingpolarized pixels in a polarization direction 0° at the time whenlinearly polarized light L90 in a polarization direction 90° isirradiated from above, that is, the front of the convex lens. Incaptured image L90C0 in the case in which an orthogonal polarized imageis observed, black regions of the black cross pattern appeared in upper,lower, left, and right positions. FIG. 10B shows captured image L135C45of a camera including polarized pixels at a polarization direction 45°at the time when linearly polarized light L135 in a polarizationdirection 135° is irradiated from the front of the convex lens. Capturedimage L135C45 also corresponds to the case in which the orthogonalpolarized image is observed. In this case, it is seen that the blackcross pattern rotates 450 with respect to FIG. 10A. Captured image L90C0corresponds to polarized image L90C0 used for synthesis by polarizedimage synthesizer 14. Captured image L135C45 corresponds to polarizedimage L135C45 used for synthesis by polarized image synthesizer 14.

FIGS. 11A and 11B are diagrams for explaining processing of polarizedimage synthesizer 14 for eliminating the black cross pattern using theprinciple of behaviors of the black cross pattern shown in FIGS. 10A and10B. FIG. 11A is a schematic diagram showing an example of theprocessing of polarized image synthesizer 14 for removing the blackcross pattern. FIG. 11B is a diagram showing an example of a periodicfunction indicating a principle of black cross pattern removal by theprocessing of polarized image synthesizer 14. As shown in FIG. 11A,polarized image synthesizer 14 acquires polarized image L90C0 andpolarized image L135C45. Polarized image L90C0 is an image generatedfrom polarized pixels in an orthogonal polarization state among imagescaptured during illumination of linearly polarized light L90. Polarizedimage L135C45 is an image generated from polarized pixels in theorthogonal polarization state among images captured during illuminationof linearly polarized light L135.

Polarized image synthesizer 14 compares, through image processing, pixelvalues in substantially the same pixel positions on the image, that is,pixel values of pixels corresponding to each other between polarizedimage L90C0 and polarized image L135C45 and selects a pixel having alarger pixel value (a brighter pixel). Polarized image synthesizer 14synthesizes, that is, generates new one image 1001 by applying the pixelselected as explained above to the pixel positions. In other words,polarized image synthesizer 14 determines a larger pixel value of thepixel value of the pixels corresponding to each other as a pixel valueof pixels of synthesized image 1001. Synthesized image 1001 is anexample of an authentication image.

In such synthesized image 1001, an iris image in which the black crosspattern is eliminated can be obtained. Polarized image L90C0 andpolarized image L135C45 are images obtained from one captured image. Thepositions of pixels of polarized image L90C0 and the positions of pixelsof polarized image L135C45 are different in the captured image.Therefore, two pixels to be compared between polarized image L90C0 andpolarized image L135C45 are located in the same position in some casesand are located near the positions of the pixels each other in othercases. For example, the two pixels to be compared may be selected frompixels in the same polarizing filter group 30 ac.

In other words, when synthesized image 1001 is represented assynthesized image Image, synthesized image Image can be generated bycarrying out processing indicated by the following Expression 1 for eachof pixels. In the following expression, “max” indicates processing forselecting larger one of two numerical values and “L90C0” and “L135C45”respectively indicate pixel values of corresponding pixels of polarizedimages L90C0 and L135C45.

Image=max(L90C0,L135C45)  (Expression 1)

Naturally, a synthesizing method for synthesized image Image is notlimited to this. For example, as indicated by the following Expression2, a pixel value may be synthesized by weighing the pixel values of thecorresponding pixels between polarized images L90C0 and L135C45 with aweight coefficient W and adding up the pixel values. The synthesizedvalue may be applied to the pixel values of the pixels of synthesizedimage 1001.

Image=W×(L90C0)+(1−W)×(L135C45)  (Expression 2)

As indicated by the following Expression 3, an average of the pixelvalues of the corresponding pixels between polarized images L90C0 andL135C45 may be calculated as, in particular, W=½. The average may beapplied to the pixel values of the pixels of synthesized image 1001.

Image=(L90C0+L135C45)/2  (Expression 3)

When phases of two periodic functions of a cycle 90° (π/2) havingamplitude A and an offset value C of luminance shift from each other by45° (π/4) as shown in FIG. 11B, from a characteristic that an average ofthe phases is just equivalent to the offset value C of the periodicfunction, luminance obtained from Expression 3 is considered to beappropriate as an estimated value of original iris luminance.

Of the two periodic functions, a periodic function indicated by L90C0indicates a periodic function concerning polarized image L90C0. Thisperiodic function indicates a change in luminance at a fixed point atthe time when a polarization direction of linearly polarized light L90of the illumination light and a polarization direction of polarizedpixel C0 are changed while maintaining a difference of 90° between thepolarization directions. The periodic function indicated by L135C45indicates a periodic function concerning polarized image L135C45. Thisperiodic function indicates a change in luminance at a fixed point atthe time when a polarization direction of linearly polarized light L135of the illumination light and a polarization direction of polarizedpixel C45 are changed while maintaining a difference of 90° between thepolarization directions. Accordingly, a difference of phases between theperiodic function of the polarized image L90C0 and the periodic functionof the polarized image L135C45 is 45° (π/4).

An iris image obtained as synthesized image 1001 is substantially equalto an iris image captured with normal unpolarized light. Therefore, itis possible to authenticate an individual having an iris usingsynthesized image 1001 and iris authentication processing in the past.

[1-3. Operation of Iris Authentication System 1]

The operation of iris authentication system 1 is explained withreference to FIG. 12. FIG. 12 is a flowchart showing an example of theoperation of iris authentication system 1 according to the firstembodiment. First, in step S1, synchronizer 11 of processor 10 causesilluminating device 20 to illuminate an authentication target person inthe front while synchronizing timing of illumination and timing ofimaging and causes camera 30 to image the target person in the front.The authentication target person may be right opposed to illuminatingdevice 20 and camera 30 or may not be right opposed to and traverseilluminating device 20 and camera 30. A captured image is an eyeballimage including an image of an eye of the authentication target personphotographed from the outer side. Synchronizer 11 causes illuminatingdevice 20 to sequentially irradiate linearly polarized light L90 andlinearly polarized light L135 and causes camera 30 to perform imagingrespectively during an irradiation period of linearly polarized lightL90 and during an irradiation period of linearly polarized light L135.Camera 30 stores two kinds of captured images in storage 12. Informationconcerning imaging time is included in the captured images.

Subsequently, in step S2, pixel selector 13 of processor 10 acquires thecaptured images from storage 12 and selects pixels in the capturedimages. Specifically, pixel selector 13 extracts, in the capturedimages, polarized pixels C0, which are pixels acquired by lightreceiving elements corresponding to first linear polarizing filters 30aca at an azimuth angle 0° of the polarization transmission axis inpolarization imaging element 30 a of camera 30, and re-accumulatesextracted polarized pixels C0 to thereby generate a polarized image,which is a new image. Pixel selector 13 extracts polarized pixels C45,which are pixels acquired by light receiving elements corresponding tosecond linear polarizing filters 30 acb at an azimuth angle 45° of thepolarization transmission axis, and re-accumulates extracted polarizedpixels C45 to thereby generate a new polarized image. Polarized imageL90C0 of polarized pixels C0 extracted from the captured images oflinearly polarized light L90, polarized image L90C45 of polarized pixelsC45 extracted from the captured images of linearly polarized light L90,polarized image L135C0 of polarized pixels C0 extracted from thecaptured images of linearly polarized light L135, and polarized imageL135C45 of polarized pixels C45 extracted from the captured images oflinearly polarized light L135 are generated. The polarized imagesinclude information concerning the polarized pixels configuring thepolarized images.

Subsequently, in step S3, polarized image synthesizer 14 of processor 10associates imaging time of captured images during illumination oflinearly polarized lights L90 and L135 acquired from synchronizer 11 andimaging time of polarized images generated by pixel selector 13 andspecifies linearly polarized lights irradiated during imaging of thepolarized images. Consequently, polarized image synthesizer 14 specifiespolarized images L90C0, L90C45, L135C0, and L135C45. Polarized imagesynthesizer 14 extracts a pair of two polarized images out of four kindsof polarized images. In the pair of the two polarized images, apolarization direction of linearly polarized light of illumination inthe polarized images and a polarization direction of the light receivingelements are orthogonal and polarization directions of the linearlypolarized lights of illumination are different between the two polarizedimages. At this time, the polarization directions of the light receivingelements are also different between the two polarized images.Accordingly, polarized image synthesizer 14 determines a pair ofpolarized images L90C0 and L135C45 as extraction targets. Further,polarized image synthesizer 14 extracts a pair of polarized images L90C0and L135C45, imaging times of which are closest to each other. Suchpolarized images L90C0 and L135C45 are images acquired in illuminationof continuous linearly polarized lights L90 and L135.

Polarized image synthesizer 14 combines extracted polarized images L90C0and L135C45. At this time, polarized image synthesizer 14 extractspixels having larger pixel values among pixels in substantially the samepixel positions between polarized images L90C0 and L135C45. Polarizedimage synthesizer 14 extracts pixels having larger pixel values in thepixel positions and accumulates the extracted pixels to thereby generatenew synthesized image 1001. Polarized image synthesizer 14 outputssynthesized image 1001 to iris authenticator 110.

Subsequently, in step S4, iris authenticator 110 collates theinformation concerning the plurality of reference images stored in irisauthentication pattern DB 120 and synthesized image 1001 to therebyidentify a user ID corresponding to synthesized image 1001. For example,by using an existing image collation technique, iris authenticator 110determines a reference image having predetermined or higher similaritywith synthesized image 1001 out of the plurality of reference images andidentifies a user ID associated with the determined reference image.Iris authenticator 110 outputs the identified user ID to output section130. When a user ID is not identified, iris authenticator 110 outputsinformation indicating impossibility of user authentication to outputsection 130.

Subsequently, in step S5, output section 130 outputs informationconcerning a user corresponding to the acquired user ID to an externaldevice such as a display device. When a user ID is not identified,output section 130 outputs information indicating impossibility of userauthentication to the external device. Output section 130 may accessnot-shown another database to thereby acquire the information concerningthe user corresponding to the user ID.

[1-4. Effects]

As explained above, image synthesizing apparatus 100 according to thefirst embodiment sequentially irradiates the two kinds of linearlypolarized lights in the different polarization directions on the eyeballof the authentication target person and performs imaging insynchronization with the irradiation to acquire two captured images.Further, image synthesizing apparatus 100 acquires a plurality ofpolarized images from the two captured images. While removing, from theplurality of polarized images, an image of specular reflection of theillumination light source due to regular reflection that occurs on theeyeglass and the cornea, image synthesizing apparatus 100 simultaneouslyremoves a black cross pattern due to birefringence on the cornea andgenerates an iris image for which iris authentication is possible. Withimage synthesizing apparatus 100, even in so-called casual irisauthentication in which the iris authentication is carried out withoutbeing aware by the authentication target person, it is possible tosimultaneously remove an image of specular reflection of theillumination light source on the eyeglass and the cornea, which is anobstacle of image processing, and an artifact due to birefringence thatoccurs on the cornea.

Second Embodiment

Image synthesizing apparatus 2100 according to a second embodiment isexplained. Image synthesizing apparatus 2100 is different from imagesynthesizing apparatus 100 in the first embodiment in the configurationsof illuminating device 220 and camera 230. Therefore, processor 210 doesnot include synchronizer. In the following explanation, differences fromthe first embodiment are mainly explained. Explanation of similaritiesto the first embodiment is omitted.

FIG. 13 is a block diagram showing an example of a functionalconfiguration of iris authentication system 2 according to the secondembodiment. FIG. 14 is a schematic diagram showing an example of a flowof processing by components of iris authentication system 2 according tothe second embodiment. As shown in FIGS. 13 and 14, iris authenticationsystem 2 includes image synthesizing apparatus 2100, iris authenticator110, iris authentication pattern DB 120, and output section 130 same asthose in the first embodiment. Image synthesizing apparatus 2100includes processor 210, illuminating device 220, and camera 230.Processor 210 includes storage 12, pixel selector 213, and polarizedimage synthesizer 214. Image synthesizing apparatus 2100 includesband-pass filter 40 between illuminating device 220 and camera 230.However, band-pass filter 40 is not essential.

As shown in FIGS. 14 to 15B, illuminating device 220 includesilluminator 220 a and polarizer 220 b. FIG. 15A is a schematic frontview of illuminating device 220 according to the second embodiment. FIG.15B is a schematic exploded view of illuminating device 220 in FIG. 15A.Illuminator 220 a includes light emitter 220 ab having a ring plateshape, on the entire surface of which a plurality of light sources 220ac are disposed, and diffusing plate 220 aa having a ring plate shapedisposed between light emitter 220 ab and polarizer 220 b. Theconfiguration of light sources 220 ac may be the same as first lightsources 20 aa and second light sources 20 ab in the first embodiment.Light emitter 220 ab is configured to cause the plurality of lightsources 220 ac to simultaneously emit lights. Consequently, lightemitter 220 ab emits ring-like illumination light toward diffusing plate220 aa. Illuminator 220 a configures a ring light of one channel.

Diffusing plate 220 aa is disposed to cover the entire plurality oflight sources 220 ac of light emitter 220 ab. Diffusing plate 220 aa andlight emitter 220 ab surround opening 220 c. Diffusing plate 220 aatransmits emitted lights of the plurality of light sources 220 ac whilediffusing the emitted lights and discharges the emitted lights towardpolarizer 220 b. Diffusing plate 220 aa may have any configuration ifdiffusing plate 220 aa has a configuration for transmitting light whilediffusing the light. Diffusing plate 220 aa converts emitted light froma point light source such as an LED into emitted light from a surfacelight source. Linearly polarized light emitted from polarizer 220 bafter being diffused by diffusing plate 220 aa can reduce luminance of abright spot of specular reflection on an eyeglass or a cornea. Further,it has been confirmed by the experiment of the inventor that, even whenan extinction ratio of a polarizing filter of polarizer 220 b is low,the linearly polarized light achieves an effect that removal of a brightspot of specular reflection of polarized light can be more effectivelyrealized. Diffusing plate 220 aa is not essential.

Polarizer 220 b includes a plurality of first polarizing filters 220 baand a plurality of second polarizing filters 220 bb disposed in a ringshape around opening 220 c. In this embodiment, two first polarizingfilters 220 ba and two second polarizing filters 220 bb are disposedalternately and adjacent to each other along the circumference ofopening 220 c. First polarizing filters 220 ba are polarizing filtershaving polarization transmission axes having an azimuth angle 0°. Secondpolarizing filters 220 bb are polarizing filters having polarizationtransmission axes having an azimuth angle 90°. The number of firstpolarizing filters 220 ba and second polarizing filters 220 bb may beany number equal to or larger than one. Disposition of first polarizingfilters 220 ba and second polarizing filters 220 bb may be anydisposition.

Light emitter 220 ab, diffusing plate 220 aa, and first polarizingfilters 220 ba functioning as first polarizing filters are located inthis order along an emitting direction of illumination light. Further,light emitter 220 ab, diffusing plate 220 aa, and second polarizingfilters 220 bb functioning as second polarizing filters are located inthis order along the emitting direction of the illumination light. Whenilluminating device 220 is viewed in a direction perpendicular to asurface on which light sources 220 ac are disposed in light emitter 220ab having the ring plate shape, that is, an optical axis of emittedlight of light emitter 220 ab, the respective sizes of light emitter 220ab, diffusing plate 220 aa, and polarizer 220 b satisfy a condition ofsize of light emitter 220 ab≤size of diffusing plate 220 aa≤size ofpolarizer 220 b. In other words, when illuminating device 220 is viewedalong the optical axis of emitted light of light emitter 220 ab, firstpolarizing filters 220 ba and second polarizing filters 220 bb aredisposed to cover entire diffusing plate 220 aa. At the same time,diffusing plate 220 aa is disposed to cover all light sources 220 ac inlight emitter 220 ab having the ring plate shape.

Illuminating device 220 explained above irradiates, on eyeball E of anauthentication target person, illumination light L obtained by mixinglinearly polarized lights in polarization directions of 0° and 90°. Thatis, illuminating device 220 simultaneously emits two kinds of linearlypolarized lights L0 and L90, the polarization directions of which areorthogonal, toward eyeball E. Return lights reflected in cornea and irisportions of eyeball E pass through opening 220 c in the center ofilluminating device 220 and are made incident on camera 230. Whenband-pass filter 40 is disposed, the return lights from eyeball E passthrough band-pass filter 40 and are thereafter made incident on camera230.

As shown in FIG. 14, camera 230 includes polarization imaging element230 a. Further, as shown in FIGS. 16A and 16B, as in the firstembodiment, polarization imaging element 230 a includes imaging element30 aa and mosaic polarizing filter 230 ab. On mosaic polarizing filter230 ab, a plurality of polarizing filter groups 230 ac are arrayed in alattice shape. FIG. 16A is a plan view schematically showing theconfiguration of polarization imaging element 230 a of camera 230according to the second embodiment. FIG. 16B is a plan view showing oneunit of groups 230 ac of polarizing filters in mosaic polarizing filter230 ab shown in FIG. 16A. Each polarizing filter group 230 ac includestwo first linear polarizing filters 230 aca and two second linearpolarizing filters 230 acb. First linear polarizing filters 230 aca andsecond linear polarizing filters 230 acb are alternately disposed in arotating direction around point P. First linear polarizing filters 230aca have polarization transmission axes having an azimuth angle 0°.Second linear polarizing filters 230 acb have polarization transmissionaxes having an azimuth angle 90°.

A light receiving element of such polarization imaging element 230 aforms a micro polarized pixel having a polarization transmission axishaving an azimuth angle 0° and a micro polarized pixel having apolarization transmission axis having an azimuth angle 90°. Camera 230can acquire, with one imaging, one captured image including polarizedpixels in two orthogonal polarization directions of 0° and 90°. That is,camera 230 can simultaneously acquire polarized images in differentpolarization directions from substantially the same visual point.

Pixel selector 213 of processor 210 re-accumulates, in the capturedimage, polarized pixels C0 acquired by light receiving elementscorresponding to first linear polarizing filters 230 aca to therebygenerate a polarized image formed by polarized pixels C0. Pixel selector213 re-accumulates, in the captured image, polarized pixels C90 acquiredby light receiving elements corresponding to second linear polarizingfilters 230 acb to thereby generate a polarized image formed bypolarized pixels C90.

Polarized image synthesizer 214 of processor 210 combines the polarizedimage formed by polarized pixels C0 and the polarized image formed bypolarized pixels C90 to generate a new synthesized image.

Reflection of illumination light on eyeball E is explained withreference to FIGS. 17 and 18. FIG. 17 is a schematic diagram showing apolarized state of reflected light at a bright spot of a specularreflection region in cornea Ea. FIG. 18 is a schematic diagram showing apolarized state of reflected light in a diffuse reflection region iniris Ec. In FIGS. 17 and 18, to simplify explanation, camera 230 andilluminating device 220 originally disposed in close positions on thesame axis are drawn to be disposed on different axes.

First, specular reflection on cornea Ea and an eyeglass surface oflinearly polarized lights L0 and L90 emitted from illuminating device220 is explained taking cornea Ea as an example with reference to FIG.17. Cornea Ea on the surface of eyeball E of the authentication targetperson has a transparent and smooth surface. Therefore, for example,linearly polarized light L0 emitted from first polarizing filter 220 bareflects at reflection bright spot BS1 on cornea Ea. At this time,according to the rule of reflection, linearly polarized light L0reflects at a reflection angle substantially the same as an incidentangle with respect to normal vector Vn1 at reflection bright spot BS1and is made incident on camera 230. Reflected light maintains apolarized state of linearly polarized light L0. Linearly polarized lightL90 emitted from second polarizing filter 220 bb reflects at reflectionbright spot BS2 different from reflection bright spot BS1 on cornea Ea.At this time, linearly polarized light L90 reflects at a reflectionangle substantially the same as an incident angle with respect to normalvector Vn2 at reflection bright spot BS2 and is made incident on camera230. Reflected light maintains a polarized state of linearly polarizedlight L90. Therefore, when illuminating device 220 is configured to emittwo kinds of linearly polarized lights L0 and L90, even if linearlypolarized lights L0 and L90 are simultaneously irradiated, therespective reflection bright spots are present in different pixelpositions on a captured image. Reflected lights maintain differentpolarized states in the pixel positions.

Reflection on iris Ec of linearly polarized lights L0 and L90 emittedfrom illuminating device 220 is explained with reference to FIG. 18. Aniris region configures a diffuse reflection region for diffusingreflected light. In reflection in the iris region, influence due toroughness of an iris surface and multiple scattering of light on asurface layer occurs. Therefore, the polarized states of linearlypolarized lights L0 and L90 are eliminated in the reflection in the irisregion. Reflected return light Lr, which is reflected light, changes toa nonpolarized state. Accordingly, an image of the iris region is in thesame state as a state in which the image is irradiated by nonpolarizedillumination. Therefore, a black cross pattern due to birefringence doesnot occur in the image of the iris region.

Further, details of processing of polarized image synthesizer 214 areexplained. FIG. 19 is a schematic diagram showing an example ofprocessing of polarized image synthesizer 214 for removing a bright spotof specular reflection. As shown in FIG. 19, in polarized image C0generated by pixel selector 213, a specular reflection image ofring-like illumination light is projected on cornea Ea of eyeball E.However, from a characteristic of camera 230, bright spot BS of only aring portion corresponding to linearly polarized light L0 emitted fromfirst polarizing filter 220 ba in the polarization direction 0° inpolarizer 220 b is observed. A bright spot of a ring portioncorresponding to linearly polarized light L90 emitted from secondpolarizing filter 220 bb in the polarization direction 90° is notobserved.

Similarly, in polarized image C90 generated by pixel selector 213,bright spot BS of only a ring portion corresponding to linearlypolarized light L90 emitted from second polarizing filter 220 bb isobserved on cornea Ea of eyeball E. A bright spot of a ring portioncorresponding to linearly polarized light L0 emitted from firstpolarizing filter 220 ba is not observed.

First, a black cross pattern due to birefringence is absent in a regionof iris Ec behind cornea Ea.

Therefore, when acquiring two polarized images C0 and C90 generated fromthe same captured image, polarized image synthesizer 214 compares,through image processing, pixel values of pixels in substantially thesame pixel positions on images between polarized images C0 and C90 andselects a pixel having a smaller pixel value (a darker pixel). Further,polarized image synthesizer 214 applies the pixel selected as explainedabove to the pixel positions to thereby synthesize new one image 2001.With such synthesized image 2001, it is possible to obtain an iris imagewith a bright spot due to specular reflection eliminated. This irisimage is substantially equal to an iris image captured by normalnonpolarized illumination. Therefore, the personal authentication usingthe iris authentication processing in the past can be applied.

As explained above, image synthesizing apparatus 2100 according to thesecond embodiment simultaneously irradiates the two kinds of linearlypolarized lights on the eyeball of the authentication target person andacquires a captured image captured by one shot. Further, imagesynthesizing apparatus 2100 acquires a plurality of polarized imagesfrom one captured image. While removing, from the plurality of polarizedimages, an image of specular reflection due to regular reflection thatoccurs on the eyeglass and the cornea, image synthesizing apparatus 2100simultaneously removes a pattern due to birefringence on the cornea andgenerates an iris image for which iris authentication is possible.Specifically, image synthesizing apparatus 2100 according to the secondembodiment mixes and irradiates spatially orthogonal linearly polarizedilluminations. Therefore, a pattern due to birefringence in the corneadoes not occur in a captured image. On the other hand, an image ofspecular reflection due to regular reflection of illumination from theeyeglass and the cornea is captured in a state in which polarization ismaintained. However, the image can be removed by image synthesizingapparatus 2100. In this way, an effect that it is possible to carry outthe iris pattern authentication in the past while removing the image ofthe regular reflection of the illumination from the eyeglass and thecornea of the eyeballs can be achieved by the imaging of the one shot.

In this embodiment, a polarization illumination apparatus is contrivedto project orthogonal two kinds of divided polarized illuminations onthe eyeball at a time. When reaching the eyeball, this light changes toa plurality of reflected images of the different polarized dividedilluminations because the light is specularly reflected on the cornea.The reflected images maintain characteristics of polarized light.Therefore, there is a first advantage that reflection can be removed byorthogonal polarizing filters and specular reflection of illuminationcan be removed. Further, in the past, when the polarized illuminationsand the polarizing filters are made orthogonal in this way, a blackcross artifact occurs on the iris because of birefringence of the corneato make it difficult to perform iris authentication. However, in thisembodiment, in light transmitted through the cornea, since differentpolarized lights scatter on an optical path and on the cornea and aremixed to be nonpolarized light. Therefore, there is a second advantagethat a black cross artifact does not occur.

Further, an advantage of one-shot imaging in this embodiment isexplained. In the casual iris authentication for the purpose of unawareauthentication, it is likely that the face and the eyeballs of a subjectare always moving. In this state, in order to carry out illumination andimaging twice to acquire two images without pixel deviation and performimage processing as in the first embodiment, it is necessary to carryout eyeball tracking to align pixels. Therefore, a pressing loadincreases. With the one-shot imaging, there is a great advantage thatthe problem of the pixel deviation is eliminated and a synchronizingdevice of illumination and imaging is unnecessary in an apparatusconfiguration.

In image synthesizing apparatus 2100 according to the second embodiment,polarized image synthesizer 214 determines, as the pixels of thesynthesized image, the pixel having the smaller pixel value (the darkerpixel) of the two pixels in substantially the same pixel positions onthe two polarized images. However, polarized image synthesizer 214 isnot limited to this. As explained in the first embodiment, polarizedimage synthesizer 214 may determine a pixel value by weighting the pixelvalues of the two pixels or may determine an average of the pixel valuesof the two pixels as a pixel value.

Third Embodiment

Image synthesizing apparatus 3100 according to a third embodiment isexplained. Image synthesizing apparatus 3100 according to the thirdembodiment is different from the image synthesizing apparatuses in thefirst and second embodiments in that illuminating device 320 irradiatescircularly polarized light. In the following explanation, differencesfrom the first and second embodiments are mainly explained. Explanationof similarities to the first or second embodiment is omitted.

A technique for irradiating circularly polarized light on an eyeball isexplained with reference to FIGS. 20A and 20B. Like FIG. 2, FIG. 20A isa diagram showing an example of the iris authenticating apparatus of therelated art for performing iris authentication using circularlypolarized light. FIG. 20B is a diagram schematically showing the detailof the optical system of FIG. 20A. The iris authenticating apparatus ofthe related art shown in FIG. 20A includes camera 30A, illuminator 320 aof nonpolarized light, and circularly polarizing plate 350.

FIG. 20A shows an overlapping state of an optical system of the irisauthenticating apparatus. When viewed from eyeball E of theauthentication target person, circularly polarizing plate 350 isdisposed in a layer close to eyeball E and ring-like illuminator 320 ais disposed in a layer farther from eyeball E. Camera 30A is a normalcamera and is disposed on the inner side of an opening of illuminator320 a. Illuminator 320 a has the same configuration as light emitter 220ab of illuminating device 220 in the second embodiment. Illuminator 320a emits nonpolarized illumination light. Circularly polarizing plate 350is not a doughnut type and covers entire illuminator 320 a. Therefore,both of incident light on eyeball E from illuminator 320 a and returnlight from eyeball E to illuminator 320 a are transmitted throughcircularly polarizing plate 350. That is, light from illuminator 320 ato camera 30A is transmitted through circularly polarizing plate 350twice in total.

The nonpolarized illumination light from illuminator 320 a is convertedinto left circularly polarized light that rotates in one direction, thatis, to the left in FIG. 20A by circularly polarizing plate 350. Thisleft circularly polarized light is irradiated on eyeball E of theauthentication target person and specularly reflected on a cornea, aneyeglass, or the like. Return light of the specular reflection changesto right circularly polarized light that rotates to the right. On theother hand, the circularly polarized light diffuses and reflects in aniris region and forms diffused reflected light. Therefore, thecircularly polarized light is eliminated by the diffuse reflection andnonpolarized return light is formed. The right circularly polarizedlight and the nonpolarized return light are made incident on circularlypolarizing plate 350 again. However, the right circularly polarizedlight rotating oppositely to the incident light is blocked by circularlypolarizing plate 350. Therefore, only a diffused reflected image of theiris is imaged by camera 30A. In this way, a birefringence pattern ofthe cornea is not generated when the circularly polarized light isirradiated on eyeball E. The diffused reflected image of the irisobtained by the diffused reflected light is equivalent to an iris imagecaptured by illumination of normal nonpolarized light. Therefore, it ispossible to perform personal authentication corresponding to a capturedimage using an image of the diffused reflected image of the iris and theiris authentication processing in the past.

However, in the related art explained above, it is necessary to selectone of right circularly polarized light and left circularly polarizedlight as illumination light of illuminator 320 a. Therefore, it islikely that a new deficiency occurs in a biological medium having acharacteristic that an optical characteristic changes between left andright circularly polarized lights, that is, a so-called circulardichromatism. Therefore, the inventor examined a configuration forequally using left and right circularly polarized lights and devisedimage synthesizing apparatus 3100 according to the third embodimentincluding an illuminating device that simultaneously illuminates leftand right circularly polarized lights.

FIG. 21 is a block diagram showing an example of a functionalconfiguration of iris authentication system 3 in the third embodiment.FIG. 22 is a schematic diagram showing an example of a flow ofprocessing by components of iris authentication system 3 according tothe third embodiment. As shown in FIGS. 21 and 22, iris authenticationsystem 3 includes image synthesizing apparatus 3100 and irisauthenticator 110, iris authentication pattern DB 120, and outputsection 130 same as those in the first embodiment. Image synthesizingapparatus 3100 includes processor 310, illuminating device 320, andcamera 330. Processor 310 includes storage 12, pixel selector 313, andpolarized image synthesizer 314. Image synthesizing apparatus 3100includes band-pass filter 40 between illuminating device 320 and camera330. However, band-pass filter 40 is not essential.

As shown in FIGS. 22 to 23B, illuminating device 320 includesilluminator 320 a and polarizer 320 b. FIG. 23A is a schematic frontview of illuminating device 320 according to the third embodiment. FIG.23B is a schematic exploded view of illuminating device 320 shown inFIG. 23A. Illuminator 320 a has the same configuration as theconfiguration of light emitter 220 ab in the second embodiment.Polarizer 320 b includes linear polarizing filter 320 b 1 same as thatof polarizer 220 b in the second embodiment and quarter wavelength plate320 b 2 (referred to as λ/4 plate 320 b 2“as well”). λ/4 plate 320 b 2is an element that sets a phase difference of λ/4, that is, 90° inorthogonal two polarization components in incident light and changes astate of incident polarized light. Linear polarizing filter 320 b 1 isconfigured by two first linear polarizing filters 320 b 1 a havingpolarization transmission axes having an azimuth angle 0° and two secondlinear polarizing filters 320 b 1 b having polarization transmissionaxes having an azimuth angle 90°. Illuminator 320 a, linear polarizingfilter 320 b 1, and λ/4 plate 320 b 2 are disposed in this order alongan emitting direction of illumination light.

First linear polarizing filters 320 b 1 a and λ/4 plate 320 b 2 covertillumination light from illuminator 320 a into right circularlypolarized light RC. Second linear polarizing filters 320 b 1 b and λ/4plate 320 b 2 converts the illumination light from illuminator 320 ainto left circularly polarized light LC. Therefore, as shown in FIG.23A, in positions corresponding to two first linear polarizing filters320 b 1 a, polarizer 320 b includes two first polarizing filters 320 ba,which are filters that have polarization transmission axes in a rightrotating direction and form right circularly polarized light RC. Inpositions corresponding to two second linear polarizing filters 320 b 1b, polarizer 320 b includes two second polarizing filters 320 bb, whichare filters that have polarization transmission axes in a left rotatingdirection and form left circularly polarized light LC. First polarizingfilters 320 ba and second polarizing filters 320 bb are alternatelydisposed in the circumferential direction of ring-shaped polarizer 320b. The number of first polarizing filters 320 ba and second polarizingfilters 320 bb may be any number equal to or larger than one.Disposition of first polarizing filters 320 ba and second polarizingfilters 320 bb may be any disposition.

Illuminating device 320 explained above can also be realized bydisposing λ/4 plate 320 b 2 between illuminating device 220 and theauthentication target person, who is an object, in illuminating device220 in the second embodiment.

Like illuminating device 220 in the second embodiment, illuminatingdevice 320 configures a ring light of one channel. Such illuminatingdevice 320 simultaneously emits left circularly polarized light LC andright circularly polarized light RC in opposite directions each otherand irradiates, on eyeball E of the authentication target person,illumination light L obtained by mixing left circularly polarized lightLC and right circularly polarized light RC. Return light reflected incornea and iris portions of eyeball E passes through opening 320 c inthe center of illuminating device 320, further passes through band-passfilter 40, and is made incident on camera 330.

As shown in FIG. 22, camera 330 includes polarization imaging element330 a. Further, as shown in FIGS. 24A and 24B, as in the firstembodiment, polarization imaging element 330 a includes imaging element30 aa and mosaic polarizing filter 330 ab. In mosaic polarizing filter330 ab, a plurality of polarizing filter groups 330 ac are arrayed in alattice shape. FIG. 24A is a plan view schematically showing theconfiguration of polarization imaging element 330 a of camera 330according to the third embodiment. FIG. 24B is a plan view showing oneunit of groups 330 ac of polarizing filters in mosaic polarizing filter330 ab shown in FIG. 24A.

Each polarizing filter group 330 ac includes two right circularpolarizing filter 330 aca and two left circular polarizing filters 330acb. An example of right circular polarizing filters 330 aca and leftcircular polarizing filter 330 acb is a circularly polarizing plate or acircularly polarizing film. Right circular polarizing filters 330 acaand left circular polarizing filters 330 acb are alternately disposed ina rotating direction centering on point P. Right circular polarizingfilters 330 aca have polarization transmission axes in a right rotatingdirection and are formed by, for example, laminating linear polarizingfilters having polarization transmission axes having an azimuth angle 0°and λ/4 plates. Left circular polarizing filters 330 acb havepolarization transmission axes in a left rotating direction and areformed by, for example, laminating linear polarizing filters havingpolarization transmission axes having an azimuth angle 90° and λ/4plates.

A light receiving element of such polarization imaging element 330 aforms a micro polarized pixel having a polarization transmission axis ina rotating direction of right circularly polarized light and a micropolarized pixel having a polarization transmission axis in a rotatingdirection of left circularly polarized light. Camera 330 can acquire,with one imaging, one captured image including polarized pixels in rightand left polarization directions. That is, camera 330 can simultaneouslyacquire polarized images in different polarization directions fromsubstantially the same visual point.

Camera 330 explained above can also be realized by disposing a λ/4 plateto cover objective lens 230 b of camera 230 between camera 230 andilluminating device 220 in camera 230 in the second embodiment. Forexample, as shown in FIG. 25, a mosaic pattern formed by light receivingelements of right and left circularly polarized lights corresponding topolarizing filter groups 330 ac of polarization imaging element 330 acan be realized without necessity of adding improvement to polarizationimaging element 230 a in the second embodiment. FIG. 25 is a diagramschematically showing a configuration of a modification of thepolarization imaging element according to the third embodiment.Specifically, a mosaic pattern corresponding to polarizing filter groups330 ac can be realized by disposing λ/4 plate 360 between polarizationimaging element 230 a and the object in the light receiving element ofpolarizing filter groups 230 ac of polarization imaging element 230 aincluding linearly polarized lights of 0° and 90°. At this time, λ/4plate 360 is disposed such that an F axis (Fast axis) and an S axis(Slow axis) of λ/4 plate 360 form an angle of 45° with respect to thepolarization transmission axis of 0° of polarizing filter groups 230 ac.

Pixel selector 313 of processor 310 re-accumulates, in a captured image,polarized pixels CR acquired by light receiving elements correspondingto right circular polarizing filters 330 aca to thereby generate apolarized image formed by polarized pixels CR. Pixel selector 313re-accumulates, in the captured image, polarized pixels CL acquired bylight receiving elements corresponding to left circular polarizingfilters 330 acb to thereby generate a polarized image formed bypolarized pixels CL. That is, accumulation processing of polarizedpixels, polarization directions of which are the same rotatingdirection, is performed and two polarized images are generated from onecaptured image.

Polarized image synthesizer 314 of processor 310 combines the polarizedimage formed by polarized pixels CR and the polarized image formed bypolarized pixels CL to generate a new synthesized image. As shown inFIG. 26, polarized image synthesizer 314 performs synthesis processingto thereby remove an image of specular reflection on the cornea or theeyeglasses from an image. FIG. 26 is a schematic diagram showing anexample of processing of polarized image synthesizer 314 for removing abright spot of specular reflection. In polarized image CR generated bypixel selector 313, a specular reflection image of ring-likeillumination light is projected on a cornea of an eyeball. However, froma characteristic of camera 330, bright spot BS of only a ring portioncorresponding to right circularly polarized light RC emitted from firstpolarizing filter 320 ba of polarizer 320 b is observed. A bright spotof a ring portion corresponding to left circularly polarized light LCemitted from second polarizing filter 320 bb is not observed.

Similarly, in polarized image CL generated by pixel selector 313, brightspot BS of only a ring portion corresponding to left circularlypolarized light LC emitted from second polarizing filter 320 bb isobserved on the cornea of the eyeball. A bright spot of a ring portioncorresponding to right circularly polarized light RC emitted from firstpolarizing filter 320 ba is not observed.

Further, in a region of an iris present behind the cornea, the rightcircularly polarized light and the left circularly polarized lightemitted from illuminating device 320 are added to each other to benonpolarized light and made incident on the eyeball. Therefore, in theiris region, a black cross pattern due to birefringence is absent.

When acquiring two polarized images CR and CL generated from the samecaptured image, polarized image synthesizer 314 compares, through imageprocessing, pixel values of pixels in substantially the same pixelpositions on images between polarized images CR and CL and selects apixel having a smaller pixel value (a darker pixel). Further, polarizedimage synthesizer 314 applies the pixel selected as explained above tothe pixel positions to thereby synthesize new one image 3001. With suchsynthesized image 3001, it is possible to obtain an iris image with abright spot due to specular reflection eliminated. This iris image issubstantially equal to an iris image captured using normal nonpolarizedillumination. Therefore, the personal authentication using the irisauthentication processing in the past can be applied.

As explained above, image synthesizing apparatus 3100 according to thethird embodiment simultaneously irradiates the two kinds of circularlypolarized lights on the eyeball of the authentication target person andacquires a captured image captured by one shot. Further, imagesynthesizing apparatus 3100 acquires a plurality of polarized imagesfrom one captured image. While removing, from the plurality of polarizedimages, an image of specular reflection that occurs on the eyeglass andthe cornea, image synthesizing apparatus 3100 simultaneously removes apattern due to birefringence on the cornea and generates an iris imagefor which iris authentication is possible. Specifically, imagesynthesizing apparatus 3100 according to the third embodiment irradiatescircularly polarized illumination and performs imaging. Therefore, apattern due to birefringence in the cornea does not occur in a capturedimage. On the other hand, an image of regular reflection of illuminationfrom the eyeglass and the cornea is captured in a state in whichcircular polarization is maintained. Therefore, the image can be removedby image synthesizing apparatus 3100. In this way, an effect that it ispossible to carry out the iris pattern authentication in the past whileremoving the image of the regular reflection of the illumination fromthe eyeglass and the cornea of the eyeball can be achieved by theimaging of the one shot.

In image synthesizing apparatus 3100 according to the third embodiment,polarized image synthesizer 314 determines, as a pixel of a synthesizedimage, a pixel having a smaller pixel value (a darker pixel) of twopixels in substantially the same pixel positions on two polarizedimages. However, polarized image synthesizer 314 is not limited to this.As explained in the first embodiment, polarized image synthesizer 314may determine a pixel value by weighting pixel values of two pixels ormay determine an average of the pixel values of the two pixels as apixel value.

Fourth Embodiment

Image synthesizing apparatus 4100 according to a fourth embodiment isexplained. In the first and second embodiments, the illuminating deviceirradiates the linearly polarized lights in the two differentpolarization directions. However, in image synthesizing apparatus 4100according to the fourth embodiment, illuminating device 420 irradiateslinearly polarized lights in four different polarization directions. Inthe following explanation, differences from the first to thirdembodiments are mainly explained. Explanation of similarities to thefirst to third embodiments is omitted.

FIG. 27 is a block diagram showing an example of a functionalconfiguration of iris authentication system 4 according to the fourthembodiment. FIG. 28 is a schematic diagram showing an example of a flowof processing by components of iris authentication system 4 according tothe fourth embodiment. As shown in FIGS. 27 and 28, iris authenticationsystem 4 includes image synthesizing apparatus 4100 and irisauthenticator 110, iris authentication pattern DB 120, and outputsection 130 same as those in the first embodiment. Image synthesizingapparatus 4100 includes processor 410, illuminating device 420, andcamera 430. Processor 410 includes storage 12, pixel selector 413, andpolarized image synthesizer 414. Image synthesizing apparatus 4100includes band-pass filter 40 as in the first embodiment. However,band-pass filter 40 is not essential.

As shown in FIGS. 28 and 29, illuminating device 420 includesilluminator 420 a and polarizer 420 b. FIG. 29 is a schematic front viewof illuminating device 420 according to the fourth embodiment.Illuminator 420 a has the same configuration as the configuration oflight emitter 220 ab of illuminating device 220 in the secondembodiment. Illuminator 420 a configures a ring light of one channel.

Polarizer 420 b includes first polarizing filter 420 ba, secondpolarizing filter 420 bb, third polarizing filter 420 bc, and fourthpolarizing filter 420 bd disposed in a ring shape around opening 420 c.In this embodiment, first polarizing filter 420 ba, second polarizingfilter 420 bb, third polarizing filter 420 bc, and fourth polarizingfilter 420 bd are disposed side by side in this order along thecircumference of opening 420 c. First polarizing filter 420 ba has apolarization transmission axis having an azimuth angle 0°. Secondpolarizing filter 420 bb has a polarization transmission axis having anazimuth angle 45°. Third polarizing filter 420 bc has a polarizationtransmission axis having an azimuth angle 90°. Fourth polarizing filter420 bd has a polarization transmission axis having an azimuth angle135°. The number of polarizers may be any number equal to or larger thanone. Disposition of the polarizers may be any disposition. An azimuthangle is defined by a camera coordinate system based on a camera.Therefore, when illuminating device 420 is viewed from the front, leftand right directions of arrows of the azimuth angles 45° and 135° arereversed.

Illuminating device 420 explained above simultaneously emits linearlypolarized lights in polarization directions 0°, 45°, 90°, and 135° andirradiates illumination light L obtained by mixing these linearlypolarized lights on eyeball E of an authentication target person. Returnlight reflected in cornea and iris portions of eyeball E passes throughopening 420 c in the center of illuminating device 420, further passesthrough band-pass filter 40, and is made incident on camera 430.

As shown in FIG. 28, camera 430 includes polarization imaging element430 a. Further, as shown in FIGS. 30A and 30B, as in the firstembodiment, polarization imaging element 430 a includes imaging element30 aa and mosaic polarizing filter 430 ab. In mosaic polarizing filter430 ab, a plurality of polarizing filter groups 430 ac are arrayed in alattice shape. FIG. 30A is a plan view schematically showing theconfiguration of polarization imaging element 430 a of camera 430according to the fourth embodiment. FIG. 30B is a plan view showing oneunit of groups 430 ac of polarizing filters in mosaic polarizing filter430 ab shown in FIG. 30A.

Each polarizing filter group 430 ac includes first linear polarizingfilters 430 aca, second linear polarizing filters 430 acb, third linearpolarizing filters 430 acc, and fourth linear polarizing filters 430acd. First linear polarizing filters 430 aca, second linear polarizingfilters 430 acb, third linear polarizing filters 430 acc, and fourthlinear polarizing filters 430 acd are disposed in this order in a rightrotating direction centering on point P. First linear polarizing filter430 aca has a polarization transmission axis having an azimuth angle 0°.Second linear polarizing filter 430 acb has a polarization transmissionaxis having an azimuth angle 45°. Third linear polarizing filter 430 acchas a polarization transmission axis having an azimuth angle 90°. Fourthlinear polarizing filter 430 acd has a polarization transmission axishaving an azimuth angle 135°.

A light receiving element of such polarization imaging element 430 aforms micro polarized pixels having polarization transmission axeshaving the respective azimuth angles 0°, 45°, 90°, and 135°. Camera 430can acquire one captured image including polarized pixels C0, C45, C90,and C135 in four polarization directions of 0°, 45°, 90°, and 135°different from one another by 45°. That is, camera 430 cansimultaneously acquire polarized images in different polarizationdirections from substantially the same visual point.

Pixel selector 413 of processor 410 re-accumulates, in a captured image,polarized pixels C0 acquired by light receiving elements correspondingto first linear polarizing filters 430 aca to thereby generate apolarized image formed by polarized pixels C0. Pixel selector 413re-accumulates, in the captured image, polarized pixels C45 acquired bylight receiving elements corresponding to second linear polarizingfilters 430 acb to thereby generate a polarized image formed bypolarized pixels C45. Pixel selector 413 re-accumulates, in the capturedimage, polarized pixels C90 acquired by light receiving elementscorresponding to third linear polarizing filters 430 acc to therebygenerate a polarized image formed by polarized pixels C90. Pixelselector 413 re-accumulates, in the captured image, polarized pixelsC135 acquired by light receiving elements corresponding to fourth linearpolarizing filters 430 acd to thereby generate a polarized image formedby polarized pixels C135. Polarized image synthesizer 414 of processor410 combines the polarized image formed by polarized pixels C0, thepolarized image formed by polarized pixels C45, the polarized imageformed by polarized pixels C90, and the polarized image formed bypolarized pixels C135 to generate a new synthesized image. As shown inFIG. 31, polarized image synthesizer 414 performs synthesis processingto thereby remove an image of specular reflection on the cornea or theeyeglasses from an image. FIG. 31 is a schematic diagram showing anexample of processing of polarized image synthesizer 414 for removing abright spot of specular reflection.

In polarized image C0 generated by pixel selector 213, a specularreflection image of ring-like illumination light is projected on thecornea of eyeball E. However, from a characteristic of camera 430, aring portion corresponding to linearly polarized light L0 emitted fromfirst polarizing filter 420 ba in the polarization direction 0° ofpolarizer 420 b is observed as extremely strong bright spot BSs. Ringportions corresponding to linearly polarized lights L45 and L135respectively emitted from second linear polarizing filters 430 acb andfourth linear polarizing filters 430 acd are observed as weak brightspots BSw. A ring portion corresponding to linearly polarized light L90emitted from third linear polarizing filters 430 acc is not observed.

Similarly, in polarized image C45, a ring portion corresponding tolinearly polarized light L45 is observed as extremely strong bright spotBSs on the cornea of eyeball E. Ring portions corresponding to linearlypolarized lights L0 and L90 are observed as weak bright spots BSw. Aring portion corresponding to linearly polarized light L135 is notobserved.

Similarly, in polarized image C90, a ring portion corresponding tolinearly polarized light L90 is observed as extremely strong bright spotBSs on the cornea of eyeball E. Ring portions corresponding to linearlypolarized lights L45 and L135 are observed as weak bright spots BSw. Aring portion corresponding to linearly polarized light L0 is notobserved.

Similarly, in polarized image C135, a ring portion corresponding tolinearly polarized light L135 is observed as extremely strong brightspot BSs on the cornea of eyeball E. Ring portions corresponding tolinearly polarized lights L0 and L90 are observed as weak bright spotsBSw. A ring portion corresponding to linearly polarized light L45 is notobserved.

Linearly polarized lights L0, L45, L90, and L135 in the fourpolarization directions of 0°, 45°, 90°, and 135° at equal intervals of45° are made incident on an iris region behind the cornea and theeyeglass. However, linearly polarized lights L0, L45, L90, and L135 formnonpolarized light by adding up one another and are made incident on theiris region as nonpolarized light. Therefore, a black cross pattern dueto birefringence is absent in an image of the iris region.

Therefore, when acquiring four polarized images C0, C45, C90, and C135generated from the same captured image, polarized image synthesizer 414compares, through image processing, pixel values of pixels insubstantially the same pixel positions on images among four polarizedimages C0, C45, C90, and C135 and selects a pixel having a smallestpixel value (a darkest pixel). Further, polarized image synthesizer 414applies the pixel selected as explained above to the pixel positions tothereby synthesize new one image 4001. With such synthesized image 4001,it is possible to obtain an iris image with a bright spot due tospecular reflection eliminated. This iris image is substantially equalto an iris image captured by normal nonpolarized illumination.Therefore, the personal authentication using the iris authenticationprocessing in the past can be applied.

As explained above, image synthesizing apparatus 4100 according to thefourth embodiment simultaneously irradiates the four kinds of linearlypolarized lights on the eyeball of the authentication target person andacquires a captured image captured by one shot. Further, imagesynthesizing apparatus 4100 acquires a plurality of polarized imagesfrom one captured image. While removing, from the plurality of polarizedimages, an image of specular reflection that occurs on the eyeglass andthe cornea, image synthesizing apparatus 4100 simultaneously removes apattern due to birefringence on the cornea and generates an iris imagefor which iris authentication is possible. In this embodiment, thenumber of polarized images generated from the same captured image islarger than the number in the second embodiment. Polarization directionsin the polarized images are different. When the number of polarizedimages to be combined increases in this way, a possibility of appearanceof an image of specular reflection of the cornea in the same position inall the polarized images decreases. Accordingly, a pixel having asmallest pixel value (a darkest pixel) among pixels in substantially thesame pixel positions on all the polarized images can accurately reflectthe iris.

In image synthesizing apparatus 4100 according to the fourth embodiment,polarized image synthesizer 414 determines, as the pixels of thesynthesized image, the pixel having the smallest pixel value (thedarkest pixel) among the four pixels in substantially the same pixelpositions on the four polarized images. However, polarized imagesynthesizer 414 is not limited to this. As explained in the firstembodiment, polarized image synthesizer 414 may determine a pixel valueby weighting the pixel values of the four pixels or may determine anaverage of the pixel values of the four pixels as a pixel value.

In image synthesizing apparatus 4100 according to the fourth embodiment,the linearly polarized lights in the four different polarizationdirections are irradiated by illuminating device 420. Polarizationimaging element 430 a of camera 430 generates the image including thepolarized pixels in the four different polarization directions. However,illuminating device 420 and polarization imaging element 430 a are notlimited to this. Illuminating device 420 only has to irradiate linearlypolarized lights in at least three different polarization directions.Polarization imaging element 430 a only has to generate an imageincluding polarized pixels in at least three different polarizationdirections. The number of polarization directions of linearly polarizedlights and the number of polarization directions of polarized pixels aredesirably the same.

[Others]

The image synthesizing apparatuses and the like according to the one orthe plurality of forms are explained above on the basis of theembodiments and the modifications. However, the present disclosure isnot limited to these embodiments and modifications. Forms obtained byapplying various modifications conceived by those skilled in the art andforms constructed by combining the components in the differentembodiments and modifications may be included in the scope of the one orthe plurality of forms without departing from the gist of the presentdisclosure.

For example, in the first to fourth embodiments, all the illuminatingdevices are explained as having the ring shape. However, theilluminating device does not always need to have a ring-likeconfiguration. The illuminating device only has to be capable ofemitting at least two polarized lights having different polarizationdirections simultaneously or one by one. For example, the illuminatingdevice may be configured by two different kinds of illuminating devicesdisposed in angle positions asymmetrically shifted from the optical axisof the camera. The two kinds of illuminating devices may sequentially orsimultaneously irradiate the eyeball of the authentication targetperson.

In the second embodiment, illuminating device 220 includes diffusingplate 220 aa between light emitter 220 ab of illuminator 220 a andpolarizer 220 b. However, diffusing plate 220 aa may be disposed in theilluminating devices in the first, third, and fourth embodiments as inthe second embodiment.

For example, in the casual iris authentication, the authenticationtarget person is imaged in a state in which a fixed distance from theauthentication target person is maintained. When ring light is used, ifthe optical axis of illumination light and the optical axis of thecamera coincide, reflected light from the retina surface returns on anoptical path of incident light. Consequently, a so-called “red eye”phenomenon occurs. The pupil does not become black and is imagedbrightly at luminance higher than luminance of the iris. In order toprevent this phenomenon, it is effective to shift the optical axis ofthe illumination light from the optical axis of the camera by a smallangle. In this case, the illumination light is not made incident on thecornea from the front of the cornea and an angle of incidence of theillumination light on a transparent medium on a cornea curved surfacechanges. Therefore, a black cross pattern shape due to birefringenceslightly changes. However, there is no problem in implementation of theprocessing of the image synthesizing apparatus.

In the fourth embodiment, illuminating device 420 emits the linearlypolarized lights in the four different polarization directions.Polarization imaging element 430 a of camera 430 acquires an image viathe four linear polarizing filters 430 aca, 430 acb, 430 acc, and 430acd having the polarization transmission axes in the differentdirections. However, illuminating device 420 and polarization imagingelement 430 a are not limited to this. The illuminating device only hasto emit at least three linearly polarized lights in differentpolarization directions. The polarization imaging element only has toacquire an image via at least three linear polarizing filters,directions of polarization transmission axes of which are different.

In the embodiments and the modifications, the azimuth angle of thepolarization transmission axis of the illuminating device is set inunits of 45°. The azimuth angle of the polarization transmission axis ofthe polarizing filter is set in units of 45°. However, the azimuthangles are not limited to this. The azimuth angles of the respectivepolarization transmission axes may be set to angles in any units. Anazimuth angle of a polarization transmission axis of an existingpolarizing plate is set in units of 45°. Therefore, when the azimuthangle of the polarization transmission axis is set in units of 45°, theexisting polarizing plate can be directly used. Accordingly, it ispossible to reduce cost.

As explained above, the technique of the present disclosure may berealized as a system, an apparatus, a method, an integrated circuit, acomputer program, or a computer-readable recording medium such as arecording disk or may be realized as any combination of the system, theapparatus, the method, the integrated circuit, the computer program, andthe recording medium. The computer-readable recording medium includes anonvolatile recording medium such as a CD-ROM.

For example, the processors included in the image synthesizingapparatuses and the like according to the embodiments and themodifications are typically realized as an LSI (Large ScaleIntegration), which is an integrated circuit. The processors may beindividually formed as one chip or may be formed as one chip including apart or all of the processors.

Circuit integration is not limited to the LSI and may be realized as adedicated circuit or a general-purpose processor. An FPGA (FieldProgrammable Gate Array) that can be programmed after LSI manufacturingor a configurable processor capable reconfiguring connection and settingof circuit cells inside the LSI may be used.

In the embodiments and the modifications, the components may beconfigured by dedicated hardware or may be realized by executingsoftware programs suitable for the components. The components may berealized by a program executer such as a processor such as a CPU readingout and executing software programs recorded in a recording medium suchas a hard disk or a semiconductor memory.

A part or all of the components may be configured from a detachable IC(Integrated Circuit) card or a stand-alone module. The IC card or themodule is a computer system configured from a microprocessor, a ROM, aRAM, and the like. The IC card or the module may include the LSI or asystem LSI. The microprocessor operates according to a computer program,whereby the IC card or the module achieves functions of the IC card orthe module. The IC card and the module may have tamper resistance.

The image synthesizing method and the like of the present disclosure maybe realized by a processor such as an MPU (Micro Processing Unit) and aCPU, a circuit such as an LSI, an IC card, a stand-alone module, or thelike.

Further, the technique of the present disclosure may be realized by asoftware program or a digital signal formed by the software program ormay be a non-transitory computer-readable recording medium in whichcomputer programs are recorded. It goes without saying that the computerprograms can be distributed via a transmission medium such as theInternet.

All of the numbers such as ordinal numbers and quantities used in theabove explanation are illustrated to specifically explain the techniqueof the present disclosure. The present disclosure is not limited to theillustrated numbers. The connection relations among the components areillustrated to specifically explain the technique of the presentdisclosure. Connection relations for realizing the functions of thepresent disclosure are not limited to this.

The divisions of the functional blocks in the block diagrams are anexample. A plurality of functional blocks may be realized as onefunctional block, one functional block may be divided into a pluralityof functional blocks, or a part of the functions may be transferred toother functional blocks. Single hardware or software may process, inparallel or in a time division manner, functions of a plurality offunctional blocks having similar functions.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The technique of the present disclosure can be widely applied totechniques for generating an image of an iris useful for irisauthentication from images including the iris. For example, thetechnique of the present disclosure can be widely used in irisauthentication techniques in fields such as driver monitoring in avehicle-mounted camera and individual specification in a signage or amonitoring camera where cooperation of an authentication target personis not easily obtained during imaging.

What is claimed is:
 1. An image synthesizing apparatus, comprising: anilluminating device that outputs linearly polarized light having a firstpolarization direction and linearly polarized light having a secondpolarization direction; a camera that captures an image in a thirdpolarization direction including a plurality of pixels and an image in afourth polarization direction including a plurality of pixels; and acontrol circuit that synthesizes, on a pixel-by-pixel basis, the imagein the third polarization direction and the image in the fourthpolarization direction into an authentication image for irisauthentication, wherein the first polarization direction, the secondpolarization direction, the third polarization direction, and the fourthpolarization direction are different from one another, and the cameraacquires the image in the third polarization direction using thelinearly polarized light in the first polarization direction andacquires the image in the fourth polarization direction using thelinearly polarized light in the second polarization direction.
 2. Theimage synthesizing apparatus according to claim 1, wherein the firstpolarization direction is different from the second polarizationdirection by 45 degrees, the third polarization direction is a lineardirection different from the first polarization direction by 90 degrees,and the fourth polarization direction is a linear direction differentfrom the second polarization direction by 90 degrees.
 3. The imagesynthesizing apparatus according to claim 1, wherein the illuminatingdevice includes: at least one first light source; at least one secondlight source; a first polarizing plate having the first polarizationdirection and located in front of the first light source; and a secondpolarizing plate having the second polarization direction and located infront of the second light source, the first light source outputs thelinearly polarized light having the first polarization direction via thefirst polarizing plate, and the second light source outputs the linearlypolarized light having the second polarization direction via the secondpolarizing plate.
 4. The image synthesizing apparatus according to claim1, wherein, when the illuminating device outputs the linearly polarizedlight in the first polarization direction, the camera captures the imagein the third polarization direction, and, when the illuminating deviceoutputs the linearly polarized light in the second polarizationdirection, the camera captures the image in the fourth polarizationdirection.
 5. The image synthesizing apparatus according to claim 1,wherein, in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to each otherbetween the image in the third polarization direction and the image inthe fourth polarization direction and determines a larger pixel value ofthe pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.
 6. The imagesynthesizing apparatus according to claim 1, wherein, in thesynthesizing of the authentication image, the control circuit comparespixel values of pixels corresponding to each other between the image inthe third polarization direction and the image in the fourthpolarization direction and determines an average of the pixel values ofthe corresponding pixels as a pixel value of a corresponding pixel inthe authentication image.
 7. An image synthesizing apparatus,comprising: an illuminating device that outputs linearly polarized lighthaving a first polarization direction and linearly polarized lighthaving a second polarization direction; a camera that captures an imagein a third polarization direction including a plurality of pixels and animage in a fourth polarization direction including a plurality ofpixels; and a control circuit that synthesizes, on a pixel-by-pixelbasis, the image in the third polarization direction and the image inthe fourth polarization direction into an authentication image for irisauthentication, wherein the first polarization direction and the secondpolarization direction are different from each other, the thirdpolarization direction and the fourth polarization direction aredifferent from each other, and the camera acquires the image in thethird polarization direction using the linearly polarized light in thefirst polarization direction and the linearly polarized light in thesecond polarization direction and acquires the image in the fourthpolarization direction using the linearly polarized light in the firstpolarization direction and the linearly polarized light in the secondpolarization direction.
 8. The image synthesizing apparatus according toclaim 7, wherein the first polarization direction is different from thesecond polarization direction by 90 degrees, the third polarizationdirection is a linear direction different from the first polarizationdirection by 90 degrees, and the fourth polarization direction is alinear direction different from the second polarization direction by 90degrees.
 9. The image synthesizing apparatus according to claim 7,wherein the illuminating device includes: at least one light source; afirst polarizing plate having the first polarization direction andlocated in front of the light source; and a second polarizing platehaving the second polarization direction and located in front of thelight source, the light source outputs the linearly polarized lighthaving the first polarization direction via the first polarizing plate,and the light source outputs the linearly polarized light having thesecond polarization direction via the second polarizing plate.
 10. Theimage synthesizing apparatus according to claim 9, further comprising adiffusing plate, wherein the diffusing plate is disposed in order of theilluminating device, the diffusing plate, and the first polarizing plateand in order of the illuminating device, the diffusing plate, and thesecond polarizing plate, and when viewed along an optical axis of theilluminating device, the first polarizing plate and the secondpolarizing plate each have a size equal to or larger than a size of thediffusing plate, and the diffusing plate has a size equal to or largerthan a size of the illuminating device.
 11. The image synthesizingapparatus according to claim 7, wherein, in the synthesizing of theauthentication image, the control circuit compares pixel values ofpixels corresponding to each other between the image in the thirdpolarization direction and the image in the fourth polarizationdirection and determines a smaller pixel value of the pixel values ofthe corresponding pixels as a pixel value of a corresponding pixel inthe authentication image.
 12. The image synthesizing apparatus accordingto claim 7, wherein, in the synthesizing of the authentication image,the control circuit compares pixel values of pixels corresponding toeach other between the image in the third polarization direction and theimage in the fourth polarization direction and determines an average ofthe pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.
 13. An imagesynthesizing apparatus, comprising: an illuminating device that outputsright circularly polarized light and left circularly polarized light; acamera that captures an image in a right polarization directionincluding a plurality of pixels and an image in a left polarizationdirection including a plurality of pixels; and a control circuit thatsynthesizes, on a pixel-by-pixel basis, the image in the rightpolarization direction and the image in the left polarization directioninto an authentication image for iris authentication, wherein the cameraacquires the image in the right polarization direction using the rightcircularly polarized light and the left circularly polarized light andacquires the image in the left polarization direction using the rightcircularly polarized light and the left circularly polarized light. 14.The image synthesizing apparatus according to claim 13, wherein theilluminating device includes: at least one light source; a rightpolarizing plate having the right polarization direction and located infront of the light source; and a left polarizing plate having the leftpolarization direction and located in front of the light source, thelight source outputs the right circularly polarized light via the rightpolarizing plate, and the light source outputs the left circularlypolarized light via the left polarizing plate.
 15. The imagesynthesizing apparatus according to claim 13, wherein, in thesynthesizing of the authentication image, the control circuit comparespixel values of pixels corresponding to each other between the image inthe right polarization direction and the image in the left polarizationdirection and determines a smaller pixel value of the pixel values ofthe corresponding pixels as a pixel value of a corresponding pixel inthe authentication image.
 16. The image synthesizing apparatus accordingto claim 13, wherein, in the synthesizing of the authentication image,the control circuit compares pixel values of pixels corresponding toeach other between the image in the right polarization direction and theimage in the left polarization direction and determines an average ofthe pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.
 17. An imagesynthesizing apparatus, comprising: an illuminating device thatsimultaneously outputs first linearly polarized light having a firstpolarization direction, second linearly polarized light having a secondpolarization direction, third linearly polarized light having a thirdpolarization direction, and fourth linearly polarized light having afourth polarization direction; a camera that captures a fifth image inthe first polarization direction including a plurality of pixels, asixth image in the second polarization direction including a pluralityof pixels, a seventh image in the third polarization direction includinga plurality of pixels, and an eighth image in the fourth polarizationdirection including a plurality of pixels; and a control circuit thatsynthesizes, on a pixel-by-pixel basis, the fifth image, the sixthimage, the seventh image, and the eighth image into an authenticationimage for iris authentication, wherein the first polarization direction,the second polarization direction, the third polarization direction, andthe fourth polarization direction are different from one another by 45degrees, and the camera acquires the fifth image, the sixth image, theseventh image, and the eighth image respectively using the firstlinearly polarized light, the second linearly polarized light, the thirdlinearly polarized light, and the fourth linearly polarized light. 18.The image synthesizing apparatus according to claim 17, wherein theilluminating device includes: at least one light source; a firstpolarizing plate having the first polarization direction and located infront of the light source; a second polarizing plate having the secondpolarization direction and located in front of the light source; a thirdpolarizing plate having the third polarization direction and located infront of the light source; and a fourth polarizing plate having thefourth polarization direction and located in front of the light source,the light source outputs linearly polarized light having the firstpolarization direction via the first polarizing plate, the light sourceoutputs linearly polarized light having the second polarizationdirection via the second polarizing plate, the light source outputslinearly polarized light having the third polarization direction via thethird polarizing plate, and the light source outputs linearly polarizedlight having the fourth polarization direction via the fourth polarizingplate.
 19. The image synthesizing apparatus according to claim 17,wherein, in the synthesizing of the authentication image, the controlcircuit compares pixel values of pixels corresponding to one anotheramong the fifth image, the sixth image, the seventh image, and theeighth image and determines a smallest pixel value among the pixelvalues of the corresponding pixels as a pixel value of a correspondingpixel in the authentication image.
 20. The image synthesizing apparatusaccording to claim 17, wherein, in the synthesizing of theauthentication image, the control circuit compares pixel values ofpixels corresponding to one another among the fifth image, the sixthimage, the seventh image, and the eighth image and determines an averageof the pixel values of the corresponding pixels as a pixel value of acorresponding pixel in the authentication image.
 21. An irisauthentication system, comprising: the image synthesizing apparatusaccording to claim 1; and an iris authentication circuit, wherein theiris authentication circuit acquires iris authentication information inwhich a plurality of user identifications (IDs) and a plurality ofreference images are associated with each other and identifies a user IDwith reference to the authentication image and the iris authenticationinformation.
 22. An image synthesizing method, comprising: sequentiallyoutputting first linearly polarized light having a first polarizationdirection and second linearly polarized light having a secondpolarization direction; when the first linearly polarized light isoutput, capturing an image to acquire a third image in a thirdpolarization direction including a plurality of pixels; when the secondlinearly polarized light is output, capturing an image to acquire afourth image in a fourth polarization direction including a plurality ofpixels; and synthesizing, on a pixel-by-pixel basis, the third image andthe fourth image into an authentication image for iris authentication,wherein the first polarization direction, the second polarizationdirection, the third polarization direction, and the fourth polarizationdirection are different from one another, and at least one of thesequential outputting, the capturing of the image to acquire the thirdimage, the capturing of the image to acquire to the fourth image, andsynthesizing is executed by at least one control circuit.
 23. The imagesynthesizing method according to claim 22, wherein the firstpolarization direction is different from the second polarizationdirection by 45 degrees, the third polarization direction is a lineardirection different from the first polarization direction by 90 degrees,and the fourth polarization direction is a linear direction differentfrom the second polarization direction by 90 degrees.
 24. The imagesynthesizing method according to claim 22, wherein, in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and a larger pixel value of the pixel values of the corresponding pixelsis determined as a pixel value of a corresponding pixel in theauthentication image.
 25. The image synthesizing method according toclaim 22, wherein, in the synthesizing of the authentication image,pixel values of pixels corresponding to each other are compared betweenthe third image and the fourth image, and an average of the pixel valuesof the corresponding pixels is determined as a pixel value of acorresponding pixel in the authentication image.
 26. An imagesynthesizing method, comprising: outputting first linearly polarizedlight having a first polarization direction and second linearlypolarized light having a second polarization direction together;capturing an image when the first linearly polarized light and thesecond linearly polarized light are output; acquiring, from the image, athird image in a third polarization direction including a plurality ofpixels and a fourth image in a fourth polarization direction including aplurality of pixels; and synthesizing, on a pixel-by-pixel basis, thethird image and the fourth image into an authentication image for irisauthentication, wherein the first polarization direction and the secondpolarization direction are different from each other, the thirdpolarization direction and the fourth polarization direction aredifferent from each other, and at least one of the outputting, thecapturing the image, the acquiring, and synthesizing is executed by atleast one control circuit.
 27. The image synthesizing method accordingto claim 26, wherein the first polarization direction is different fromthe second polarization direction by 90 degrees, the third polarizationdirection is a linear direction different from the first polarizationdirection by 90 degrees, and the fourth polarization direction is alinear direction different from the second polarization direction by 90degrees.
 28. The image synthesizing method according to claim 26,wherein, in the synthesizing of the authentication image, pixel valuesof pixels corresponding to each other are compared between the thirdimage and the fourth image, and a smaller pixel value of the pixelvalues of the corresponding pixels is determined as a pixel value of acorresponding pixel in the authentication image.
 29. The imagesynthesizing method according to claim 26, wherein, in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the third image and the fourth image,and an average of the pixel values of the corresponding pixels isdetermined as a pixel value of a corresponding pixel in theauthentication image.
 30. An image synthesizing method, comprising:outputting right circularly polarized light and left circularlypolarized light together; capturing an image when the right circularlypolarized light and the left circularly polarized light are output;acquiring, from the image, an image in a right polarization directionincluding a plurality of pixels and an image in a left polarizationdirection including a plurality of pixels; and synthesizing, on apixel-by-pixel basis, the image in the right polarization direction andthe image in the left polarization direction into an authenticationimage for iris authentication, wherein at least one of the outputting,the capturing, the acquiring, and synthesizing is executed by at leastone control circuit.
 31. The image synthesizing method according toclaim 30, wherein, in the synthesizing of the authentication image,pixel values of pixels corresponding to each other are compared betweenthe image in the right polarization direction and the image in the leftpolarization direction, and a smaller pixel value of the pixel values ofthe corresponding pixels is determined as a pixel value of acorresponding pixel in the authentication image.
 32. The imagesynthesizing method according to claim 30, wherein, in the synthesizingof the authentication image, pixel values of pixels corresponding toeach other are compared between the image in the right polarizationdirection and the image in the left polarization direction, and anaverage of the pixel values of the corresponding pixels is determined asa pixel value of a corresponding pixel in the authentication image. 33.An image synthesizing method, comprising: simultaneously outputtingfirst linearly polarized light having a first polarization direction,second linearly polarized light having a second polarization direction,third linearly polarized light having a third polarization direction,and fourth linearly polarized light having a fourth polarizationdirection; capturing an image when the first linearly polarized light,the second linearly polarized light, the third linearly polarized light,and the fourth linearly polarized light are output; acquiring, from theimage, a fifth image in the first polarization direction including aplurality of pixels, a sixth image in the second polarization directionincluding a plurality of pixels, a seventh image in the thirdpolarization direction including a plurality of pixels, and an eighthimage in the fourth polarization direction including a plurality ofpixels; synthesizing, on a pixel-by-pixel basis, the fifth image, thesixth image, the seventh image, and the eighth image into anauthentication image for iris authentication, wherein the firstpolarization direction, the second polarization direction, the thirdpolarization direction, the fourth polarization direction are differentfrom each other by 45 degrees, and at least one of the simultaneouslyoutputting, the capturing, the acquiring, and synthesizing is executedby at least one control circuit.
 34. The image synthesizing methodaccording to claim 33, wherein, in the synthesizing of theauthentication image, pixel values of pixels corresponding to oneanother are compared among the fifth image, the sixth image, the seventhimage, and the eighth image, and a smallest pixel value among the pixelvalues of the corresponding pixels is determined as a pixel value of acorresponding pixel in the authentication image.
 35. The imagesynthesizing method according to claim 33, wherein, in the synthesizingof the authentication image, pixel values of pixels corresponding to oneanother are compared among the fifth image, the sixth image, the seventhimage, and the eighth image, and an average of the pixel values of thecorresponding pixels is determined as a pixel value of a correspondingpixel in the authentication image.
 36. An iris authenticating method,comprising: acquiring the authentication image generated by the imagesynthesizing method according to claim 22; acquiring iris authenticationinformation in which a plurality of user IDs and a plurality ofreference images are associated with each other; identifying a user IDwith reference to the authentication image and the iris authenticationinformation, wherein at least one of the acquiring of the authenticationimage, the acquiring of the iris authentication information, and theidentifying is executed by at least one control circuit.